md5^-1(hash)
I just came across this website: http://md5.rednoize.com, http://md5.cryptobitch.de, http://passcracking.com They have a large dictionaries of unsalted MD5/SHA passwords. I played with it for a little bit. It’s amazing and scary how little entropy there is in a simple dictionary-based passwords with few modifications! Another conclusion is that you should never use unsalted passwords in your programs.