It all happened to us at least once: losing a Microsoft product key, either by carelesness, the cleaning corporation, or a sudden fireball in your drawer. It's not so much a problem if your system is still operational, but what to do when you have to reinstall your computer? One can't just buy expensive licenses all over again, now can we?
Fortunately, there are tools out there that allow the retrieval of product keys, as long as they are installed. ProduKey, created by Nirsoft is one such program. It quickly retrieves product keys from a working system for Windows, Office, SQL server and other Microsoft products.
Direct download link: http://www.nirsoft.net/utils/produkey.zip.