Google Adwords Keyword Tool
KeyworDiscovery
WordTracker
KeywordElite

IBP
A1 Sitemap Generator
Xenu Broken Links Finder
Comment Kahuna Blog Finder

Firebug
SeoQuake
SEO for Firefox

This tool shows all the domains linking to your site according to Yahoo search engine.
This tool shows the actual pages linking to your site, and not only doamins.