ProduKey is a small utility that displays the ProductID and the CD-Key of MS-Office, Windows, Exchange Server, and SQL Server installed on your computer. You can view this information for your current running operating system, or for another operating system/computer - by using command-line options. This utility can be useful if you lost the product key of your Windows/Office, and you want to reinstall it on your computer.
* New option: Load the product keys of external Windows installations from all disks currently plugged to your computer. When using this option, ProduKey automatically scan all your hard-drives, find the Windows installation folder in them, and extract all product keys stored in these Windows installations.
* New Command-Line Option: /external
Tools and Utilities
Product page: here