Here's a suite of some free SEO tools I use:
GooglebotSpoofer Gives your website as seen by Googlebot and other search engine robots.
iWebTool A suite of tools to check your PR, keyword density, link populairty, backlinks etc
GoogleRankings Check your ranking on Google, MSN and Yahoo for up to the 1000th SER! (this one saved me loads of time).
Anyone else has other cool SEO tools to share with us? 8)