The following are cracker applications that we use in our testing:

L0phtCrack
This is a commercial tool that provides dictionary, brute force, and hybrid attacks against both Windows and Unix password hash files.  It also has the ability to capture the Windows password hash file when installed on the network with Administrative credentials.  Lophtcrack provides good reporting options and has some support for rainbow tables.

http://www.l0phtcrack.com/

ophcrack
This is an open-source tool that focuses solely on using rainbow tables to crack Windows password hash files.  It comes with a few free pre-generated hash tables that are effective against most Windows passwords.  More advanced and complex pre-generated hash tables are available for a fee.

http://ophcrack.sourceforge.net/