Enchanted Keyfinder quickly discover or change your Windows and Office product keys
Enchanted Keyfinder, which is free, open-source, and only 400KB big, does just two things: it shows you the product keys for your Windows (95, 98, ME, NT, 2K, XP, Vista and 7) and Office (2007 and 2010) installations -- and in the case of Windows XP, it also lets you change your product key. If you have a broken Windows installation, you can also use Enchanted Keyfinder with a Linux live CD; neat. There's also the option to export your product keys to a flat text file, which is probably a good idea!
In the next version, the developer wants to add remote registry access, which could be a handy tool for a system administrator. He also wants to add serial key snooping for other programs. Incidentally, if you're looking for a tool that can extract product keys from programs like Photoshop and Dreamweaver, Softkey Revealer is still going strong!