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As with many of these applications, you should avoid using your machine while LCP recovers passwords, as it will consume the majority of your machine resources for the crack.
Ophcrack is one of the most popular password recovery tools. It's free (open source as well), cross platform, and very reliable. Ophcrack uses a solid implementation of rainbow tables that just happens to have been done by those who created the method.
Ophcrack runs on Windows, Linux/UNIX, and Mac. It cracks LM and NTLM hashes; has free tables for XP, Vista, and 7; includes a brute-force module for simple passwords; offers an audit mode and a CSV export; presents real-time graphs; has a LiveCD for easier (and more efficient) recovery; and dumps and loads hashes from encrypted SAM.