- Recover Windows 95/98/ME/2000/XP/2003/Vista/7 32-bit(x86) product keys.
- Recover Microsoft Office XP/2003/2007 product keys.
- Recover over 700 software product keys.
You can view this information for your current running operating system, or for another operating system/computer - by using command-line options.
The Nirsoft site has a wealth of free and extremely useful Windows-related utilities and is well worth exploring if you like that kind of thing.
Magical Jelly Bean Keyfinder
If the free utilities above can't recover the key you need, then you may want to look at the shareware Recover Keys utility, which can check for over 1,100 product keys.