Ophcrack is a free Windows password cracker based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method. It comes with a Graphical User Interface and runs on multiple platforms.
Features:

* » Runs on Windows, Linux/Unix, Mac OS X, …
* » Cracks LM and NTLM hashes.
* » Free tables available for Windows XP and Vista.
* » Brute-force module for simple passwords.
* » LiveCD available to simplify the cracking.
* » Loads hashes from encrypted SAM recovered from a Windows partition, Vista included.
* » Free and open source software (GPL).