Brutus

Brutus : A network brute-force authentication cracker
This Windows-only cracker bangs against network services of remote systems trying to guess passwords by using a dictionary and permutations thereof. It supports HTTP, POP3, FTP, SMB, TELNET, IMAP, NTP, and more. No source code is available. UNIX users should take a look at THC Hydra.

RainbowCrack

RainbowCrack : An Innovative Password Hash Cracker
The RainbowCrack tool is a hash cracker that makes use of a large-scale time-memory trade-off. A traditional brute force cracker tries all possible plaintexts one by one, which can be time consuming for complex passwords. RainbowCrack uses a time-memory trade-off to do all the cracking-time computation in advance and store the results in so-called “rainbow tables”. It does take a long time to precompute the tables but RainbowCrack can be hundreds of times faster than a brute force cracker once the precomputation is finished.

Pwdump

Pwdump : A window password recovery tool
Pwdump is able to extract NTLM and LanMan hashes from a Windows target, regardless of whether Syskey is enabled. It is also capable of displaying password histories if they are available. It outputs the data in L0phtcrack-compatible form, and can write to an output file.

L0phtcrack

L0phtcrack : Windows password auditing and recovery application
L0phtCrack, also known as LC5, attempts to crack Windows passwords from hashes which it can obtain (given proper access) from stand-alone Windows NT/2000 workstations, networked servers, primary domain controllers, or Active Directory. In some cases it can sniff the hashes off the wire. It also has numerous methods of generating password guesses (dictionary, brute force, etc). LC5 was discontinued by Symantec in 2006, but you can still find the LC5 installer floating around. The free trial only lasts 15 days, and Symantec won’t sell you a key, so you’ll either have to cease using it or find a key generator. Since it is no longer maintained, you are probably better off trying Cain and Abel, John the Ripper, or Ophcrack instead.

THC Hydra

THC Hydra : A Fast network authentication cracker which support many different services
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. Like THC Amap this release is from the fine folks at THC.

John the Ripper

John the Ripper : A powerful, flexible, and fast multi-platform password hash cracker
John the Ripper is a fast password cracker, currently available for many flavors of Unix (11 are officially supported, not counting different architectures), DOS, Win32, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types which are most commonly found on various Unix flavors, as well as Kerberos AFS and Windows NT/2000/XP LM hashes. Several other hash types are added with contributed patches. You will want to start with some wordlists, which you can find here, here, or here.

Cain and Abel

Cain and Abel : The top password recovery tool for Windows
UNIX users often smugly assert that the best free security tools support their platform first, and Windows ports are often an afterthought. They are usually right, but Cain & Abel is a glaring exception. This Windows-only password recovery tool handles an enormous variety of tasks. It can recover passwords by sniffing the network, cracking encrypted passwords using Dictionary, Brute-Force and Cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords, revealing password boxes, uncovering cached passwords and analyzing routing protocols. It is also well documented.