I recently ran across a free open source utility called Keyfinder that extracts license keys for the software you have installed on your computer. You can find more information and download it from http://magicaljellybean.com/keyfinder/. [more]
There is a configuration file that indicates where in the registry the key is located for various products - it can be expanded for additional products. You can also load the hive from another drive if you have an accessible drive from another system and need the keys for software that was installed on it.