Link popularity is possibly the number one concern for those seeking to optimize there search engine results. There is possibly nothing more important than raising link popularity as much as your can, apart from fresh content to keep your regulars happy.

Link Popularity.com - simple tool showing the results on the big three.

Link Pop Checker - outstanding link popularity tool for checking a single page. Compares your results, to three others of your choosing.

Google Link Popularity - another excellant free tool that gives you lots of interesting information.123 Promotion - generates a list of keywords based on your content.

PR Search Link Pop - quick and easy tool for checking backlinks in the major search engines.

In terms of commercial tools, there are several:

and:

Web CEO has probably the best overall set of tools for search engine optimization around, and considering something like 130,000 people are using there software, you know your in the right hands.