A quick bump because I didn't want to see this thread archived, maybe we can keep this updated. Lots of good stuff here, everyone who contributed should be commended.
RockXP allows you to retrieve your XP product key that you used when you installed Windows XP, as well as keys for other Microsoft products. This can come very handy if you need to reinstall but have misplaced or lost the CD cover with the serial sticker. In addition, the program also lets you save the product activation to a file, and enables you to recover usernames and passwords contained in the Windows Secure Storage.
If your trying to get rid of Winfixer 2005, the manual removal method is detailed on this site with a link to Spy Sweeper, which does it automagically. Spy Sweeper has a free trial on the download page.