I only use a few key tools, but there are loads of new tools to use. The best thing to do is to find sites that assist your SEO methods rather than reply on tools that in my experience only exist to make someone richer selling methods that are free!!
I only use SEOBOOK Tools for checking Cache and Page rank. Its really Good in checking the Alexa Ranking and others. Thanks, Atechnocrat Web Solution
SEO Powersuite for analyzing absolutely everything. It also prints and publishes detailed reports for our clients.
There are many SEO tools to use, check your backlinks with various sources, use the Google Keyword Tool, and Google Webmaster Central can be a huge help