ophcrack

Ophcrack is a free rainbow-table based cracker for Windows passwords (though the tool itself runs on Linux, Windows, and Mac). Features include LM and NTLM hash cracking, a GUI, the ability to load hashes from encrypted SAM recovered from a Windows partition, and a Live CD version. Some tables are provided as a free download but larger ones have to be bought from Objectif Sécurité.

THC Hydra

When you need to brute force crack a remote authentication service, Hydra is often the tool of choice. It can perform rapid dictionary attacks against more then 30 protocols, including telnet, ftp, http, https, smb, several databases, and much more.

John the Ripper

John the Ripper is a fast password cracker for UNIX/Linux and Mac OS X.. Its primary purpose is to detect weak Unix passwords, though it supports hashes for many other platforms as well........