I do SEO and a Marketing Specialist for a large web design firm. I find that there are a lot of great FREE resources out there and I've found some great ones. Here is the list of free tools I use on a regular basis, from developing a site to SEO stuff:

http://www.gorank.com/seotools/
http://www.searchengineworld.com/cgi-bin/kwda.cgi
http://www.marketleap.com/publinkpop/default.htm
http://www.content.overture.com/d/USm/ac/index.jhtml
http://www.langreiter.com/exec/yahoo-vs-google.html
http://www.yahoo-watch.org/cgi-bin/proxy.htm
http://rankwhere.com/google-page-rank.php
http://googlerankings.com/
http://www.digitalpoint.com/tools/
http://ranking.thumbshots.com/
http://www.seo-guy.com/seo-tools/google-pr.php

Some of these will come and handy and some won't. I'll let you be the judge of how you can benefit from the tools listed. I hope you can use the tools!