Pros:  My favorite keyfinder No software installation Open Source

Cons:  Has some bugs such as listing blank keys (like Half-Life) when the program is not installed.

Other Thoughts:  At one point in time Magical Jelly Bean Keyfinder was open sourced using the GPL. I got a hold of those sources and have continued the community project.

I created the Enchanted Keyfinder. I added many features and fixed many bugs since MJB Keyfinder 2.0.8.

Here is a description from the project page and a list of features.
Enchanted Keyfinder is a Magical Jelly Bean Keyfinder fork. It is a utility that retrieves the product key used to install Windows from your registry or from an unbootable Windows installation. It works on Windows 9X, ME, NT/2K/XP, and Vista/Win7 and for other software.
- Office 2010, Office 2007, Vista, & Windows 7 support
- Change Windows Registration information and Product Key
- Portable, settings saved in an INI file
- An optional config file for software serial lookups
- Load a registry hive backup
- Can check for program and config file updates
- Command line options
- No software installation

I also give out the original MJBKF 2.0.8 and 2.0.1 open source editions, citing roots.

Download the latest Enchanted Keyfinder.
http://sourceforge.net/projects/keyfinder/files/latest

Check out my development plans for the project.
http://sourceforge.net/apps/phpbb/keyfinder/viewtopic.php?f=1&t=5