Md5

http://md5.crysm.net/ useful for simple things; some cool links

http://www.cs.colorado.edu/~jrblack/papers/cbh.html#henson a paper by J. Black (U of Colorado) addressing some concerns about compare/address-by-hash methods. Those concerns are frequently razed by Val Henson

http://www.lightbluetouchpaper.org/2007/11/16/google-as-a-password-cracker/ cracking md5’s by a google search – very smart!