Web Rank Info: Web Rank Info offers a free web based PageRank estimation tool. While I am not sure how exactly they compile this data, it is rather acurate. It also approximates the PageRank out to two decimal points.
Optilink: Optilink is link analysis software which has the ability to organize search results based on Google PageRank. Obviously this is against the Google Terms of Service, but many SEO's and professional webmasters use this software to speed up the link generation process.

Once you know how Google measures or evaluates your links then you will be in a better position to conduct a more effective link campaign. Before I explain the current pattern of link evaluation let's take a stroll down memory lane to see how far things have come.

In The Beginning A link Was The Equivalent Of A Thumbs Up Vote!

The original premise of the internet was to have a bunch of related resources (websites) linking to one another in a natural pattern of progression. Thus someone on a website focusing on gorillas for example would then naturally migrate from that site to one that listed gorilla safaris. Thus quite soon links became (and still are) the standard with which to measure a website's relevance.

The thinking behind this was that the more popular a website was the greater the likelihood that people would link to it; and since people would only tend to link to sites that offered useful information then it naturally followed a large number of links signified quality...at least that was the idea.

The Birth of Link Spam!

Soon enough wily webmasters realized that they could manipulate the linking concept to their own advantage and make a handsome profit while they were at it. Instead of waiting for people to link to their new sites (a process that could take forever) why not form link directories whereby one, for a certain fee, could amass a large number of links in next to no time at all!

Booming Link market

Getting a new website indexed by Google used to be a task of Herculean proportions. Quite often new websites would languish in obscurity for ages, but those in the know realized that the process could be accelerated. By linking a new website to an established website or webpage with a high page rank (typically page rank (PR) 7 and above) that new website could be indexed by Google within days or a matter of hours depending on the PR value of the webpage on which the link was located. However getting a link from a high PR webpage did not come cheap and it was not uncommon for webmasters to fork over $800 for a one month link on a PR8 webpage!

Debut of The Link Farm

The link market trade flourished for a while, making a mockery of Google's system of assessing the importance of any given website or webpage. However, a lot of webmasters in a hurry to see their websites scramble up the search engine indexes could not afford the hefty price commanded by a link from a high PR webpage and thus link farms came into being.

Link farms were the poor man's solution to the hefty priced, high value links typical of high PR webpages. The premise of the link farm was as follows: instead of paying an outrageous sum of money for one link from a high page rank website why not pay a small fee for thousands of low PR links? In essence the link farms abided along the principle of the sum amounting to greater than its individual parts!

The Obsession With The PR Band!

Google thoughtful as ever, made it possible for anyone to determine the relative importance of a website at a glance. This they did by the introduction of the PR band, a small line atop one's browser fittingly entitled with the word "PageRank." The pagerank band scaled from a low of zero (PR0) to a high of ten (PR10). The greater the value that Google attributed to a given webpage the higher its designated page rank. In little to no time at that little green slash (PR band) became the highly effective unofficial publicist for the flourishing link market trade.

Webmasters obsessed over the PR band even though in truth the page rank value of a webpage plays little to no part in determining the position any webpage will attain on the SERPs (search engine index results pages). However savvy marketers used the PR obsession of the day to great advantage...using it as a tool to establish credibility and ultimately sell their wares to the less savvy.

However somewhat on par with the abuse of the linking system, the page rank concept soon became equally defunct. In no time at all the Google index was awash with spam sites topping its front page! Something had to give; and it did!

Fast Forward To Today...New Link Evaluation Parameters!

Oh how times have changed!

The search engine algorithms have gotten so much smarter that even blackhat SEO (shady search engine optimization techniques) these days is more trouble than its worth. With the continued abuse and manipulation of the system Google furiously tackled the issue of how to maintain website relevance and quality in its index in an increasingly spammy world.

Since its embracement by the public, the internet has seen its fair share of SEO manipulation from blackhat techniques such as multiple-blog-creation software following the debut of blogs (principle behind this system was that one could create thousands of instant one-way backlinks through the instant generation of thousands of blogs) to whitehat techniques such as the widespread dissemination of articles through article distribution software or services.

Some of these techniques still have value today while others have been effectively nullified such as the mass generation of backlinks through the creation of instant blogs.

How Google Currently Evaluates Links.

It used to be that if the PR band of your website/webpage was gray then this signified that said webpage had been banned. That is no longer the case. All new websites/webpages start off with a grayed out PR band. This band will remain that color depending on a number of factors before it turns white (indicating that the probationary period is over) and eventually transforms to green with establishment of page rank above zero.

Link Aging Filter / Link Probation Period

To counter the widespread habit of acquiring links for a short-term period, say a month, so as to get a website indexed or attain page rank quickly, Google now subjects every link to a probationary period in which time the link is identified by Google but not accorded any value. Although such a link is recognized by Google, typically it will not be registered as a link associated with the website to which the link points for a subjective period; for that to happen the link needs to mature, and the rate at which a link matures is dependent on a number of factors.

Factors That Hasten Link Maturity Or Reduce Link Probationary Period

1. Keywords: The keyword incorporated in any given link is going to determine how long that link will be under probation. The more competitive the keyword the longer will be the link's probationary period. In reality this link probationary system has superseded the Google Sandbox, which was/is Google's technique of ensuring that super-optimized new sites do not zoom uncontrollably up the SERPs, quickly overshadowing long established websites. With respect to the Google Sandbox concept, if a new website was/is targeting a very competitive market already saturated with millions of sites, then that new website would spend a longer period cooling its heels in the Google Sandbox.

2. Volume of Traffic Across A Link: The more trafficked a link is, the quicker it will attain full SEO-value recognition by Google. This is a relatively new system in play and basically what it means is that a heavily trafficked low PR link will bestow far more SEO influence to the webpage it points to than a little trafficked high page rank link. In essence Google has pretty much nullified the system whereby webmasters could purchase links from high PR webpages in hopes of improving the SEO status of their own site. The application of this system explains why some newer webpages attain PR before older more established webpages on the very same website.

3. Links From Topically Related Sites: A links that comes from a website or webpage that has a comprehensively topical relationship to the destination webpage will have greater value than a link that does not. For example, say your website is about internet marketing, getting a link from another website that focuses on online marketing software would definitely fall under the category of topically related sites.

4. Utilizing Different Keywords In Links: Having the same keyword incorporated within all the links pointing to your site will tend to set off red flag alerts, which means that those links are not going to attain full SEO-value recognition by Google for a longer duration. Another link strategy you should employ is to have your links pointing to some of your inner pages as opposed to all your links pointing to your home page. Having links spread across multiple webpages registers as a more natural link strategy to the Google algorithm and the premise of this algorithm tweak was to nullify the system where webmasters would purchase links from link directories.

Remember anything that appears suspicious to the Googlebot is ultimately going to decrease the effectiveness of your SEO campaign. There're many more factors that play a role in determining how high and how fast your website will make it up the SERPs (Google of course doesn't spill all the beans) but if you conduct your link campaign with these few tips in mind you won't go far wrong.

What is a quality incoming link? This article describes the key characteristics of a perfect link. For explanation purposes, the sample company is a shoe retailer called Fred's Sports, and the keyword phrase being optimized for is "blue Nike sneakers".

Key word phrase in anchor text

Unless you put your keyword phrase in the anchor text (the text that describes the web site being linked to), you are wasting a lot of link power. Unfortunately a lot of people don't know this an end up putting their company name in the link text rather than the keyword phrase that they want their company to be found by. Much better that they link anchor says "blue Nike sneakers" than "Fred's Sports Store".

The link is from a relevant page

Google and the Google-powered search partners seek relevance in the interconnectedness of web pages. Incoming links should be from pages where the content on that page is related to the content of the page that is being linked to. A fishing related page linking to a casino site is an example of a non-related link. A jogging related page linking to a blue Nike sneakers product page is related and is looked upon favourably by the search engines.

The link goes to a relevant page

Another mistake that people make is always linking to the home page rather than to the most relevant page to the anchor text. If the link anchor text is "blue Nike sneakers" then the link should go to a page about blue Nike sneakers, not the home page. This is by far and away the most common linking mistake.

The link is from an authority site

Links from high Google PageRank sites are worth more, a lot more, than links from other sites. It's all about trust. A link from a trusted site tells the search engines that the sites linked to are also trusted - it's a vote of confidence from a credible source. Links from .gov, and .edu sites are also reported as having more weight than standard links. They are also more difficult to get adding to their perceived quality.

The link is at top of the page

Links from the top of a page (except for the header), are said to have more weight than links at the bottom of pages. It's the same with keyword phrases. A keyword phrase in the heading is worth more than in the body text.

The link is one-way, not reciprocal

Google's algorithm looks for link exchanges between sites and rates these links lower than straight one-way links. If possible, look for one way links by creating link bait - compelling content that will encourage people to link to your pages.

The link is within the body copy - not an advertising zone

Linking should be a natural part of the body copy. Recent reports suggest that the search engines will derate links from parts of the page that are traditionally sold for advertising. these tend to be the margins, header and footer areas of the page.

The link does not have a nofollow tag

The nofollow tag is a recent innovation that tells the search engines that although I am linking to this other page, I do not vouch for the page's integrity. In short, the nofollow tag tells the search engines to ignore the link. Obviously you do not want links to your web pages to have nofollow tags. Be careful with link exchanges. Some dishonest people will exchange links with you but use nofollow tags in the links to your pages to preserve their own link power.

There are few links on page (less than 20)

One link to your web site from a page with hundreds of links does little for your SEO results. The page's SEO power is being distributed over all the other links on the page. Goo;le's guidelines recommend no more than 100 links per page, but I believe 20 is a reasonable goal. You never know when the Google algorithm may change. The perfect page that links to your pages should have no more than 20 links.