SEO Quake
http://www.seoquake.com/index-en.php
sits at the top of your browser window,and when expanded it shows pages index, links t that page, and links to that domain in various serach engines

Also has links to whois, arrchive.org, alexa ranking, keyword density counters and a basic reverse IP lookup.

This and seobook.com have been making my life much more productive this week so I thought I'd spread the love.