MD5 – while not really crackable, it should be realised that it is just too easy to find simple passwords from the raw hash using Rainbow Tables.
Rainbow tables are massive collections of hashes derived from possible passwords. The rainbow table method simply compares the computed hases against your hash and if you are (un)lucky you will get the password.
Here is a sample of MD5 search sites, that will allow you test the strength of your MD5 passwords.
http://gdataonline.com/seekhash.php
http://md5.rednoize.com/
http://www.md5search.de/
Keep the passwords complicated, and if you are writing web apps, please use a salt!
