Search: Google, Bing, Yahoo,
Mail: Live, GMail, Roadrunner,
Social: delicious, twitter, linkedin, facebook
References: phone search, dictionary, grammar, maps, weather, radar
Support: DNSStuff, Netcraft, ServerMojo, Browser Stats, What Is My IP, MyBrowserInfo
Generators: GUID, Lorem Ipsum, Random Text, Random List, Passwords, Strings,
Domains: bustaname.com, namestation.com,
Validators: XHTML, W3C RSS, RSSBoard.org
References: HTTP Error Codes, SMTP Error Codes, Unix Commands, MIME Types, Roman Numerals, ASCII,
Calculators: Calculators/Converters, File Transfer Time, Broadband Speed
CSS v2, Javascript, HTML ( Entities), RGB, RegEx, MSSQL, XSLT
...by the way, Cheat Sheets rocks!!