Ophcrack is a Windows Password cracker based on Rainbow Tables.
http://null-byte.wonderhowto.com/how-to/hack-windows-7-become-admin-0160151/
This is a nice exploit that does not require a boot usb or CDROM. See comments and linked articles for more options.
Offline Windows Password & Registry Editor
[Long Passwords Comic] (https://qph.is.quoracdn.net/main-qimg-eefe9d8c61eff800ba25e83d23911a9a?convert_to_webp=true)
Cain & Abel is a password recovery tool for Microsoft Operating Systems.
I don’t think this one works as the author describes it.
http://www.davidtan.org/hacking-cracking-windows-xp-login-password/
This tool reportedly allows retrieval from RAM of the current user’s Windows password.
https://github.com/gentilkiwi/mimikatz/blob/master/README.md
superuser insights:
http://superuser.com/questions/235300/where-does-windows-os-store-user-passwords
http://superuser.com/questions/118233/how-are-windows-passwords-handled
http://m.windowsecurity.com/articles-tutorials/authentication_and_encryption/How-Cracked-Windows-Password-Part2.html