PK Finder is a free application that can help you recover your Windows Product Key in case you forgot it, are unable to access it, or simply for testing purposes.
WinProdKeyFinder is a straightforward, portable app to retrieve Windows product key including the ability to decode your key from your DigitalProductId value.
AlphaComps KeyViewer is a classic freeware app to retrieve your Windows and Office product key as well as decode the RawKey from your DigitalProductId.