If you are looking to do search engine optimization this section may provide some help. Listed below are tools that give you insight on search terms and others give you an idea of how well optimized your site is.

research or for improving the optimization of your website.

GoogSpy - If you are interested in finding out what search terms your competition is ranked for or is adverting on, then this site will be a great tool for you.
SEOMOZ's Tools
Wordtracker - This is a keyword research tool that tells you the popularity of certain keywords across the major search engines. It also gives you suggestions on other related terms that are high and low in traffic.
Search Term Suggestion - This tool comes directly from Yahoo and it gives you an idea on how popular search terms are. This gives you good input on what terms you want your site to be optimized for. Be careful because the total number does not mean that a high ranking for that keyword will get you that amount of traffic.
Meta Tag Analyzer
Google Toolbar - If you want to find out your site's Google PageRank you will need to install this toolbar. It will show you your PageRank, but be careful because it is not frequently updated.
Digital Point SEO Tools