Platform: Windows XP
Number of downloads: 4244
HijackThis will scan your PC and list every single browser add-on, plug-in and start-up item on your PC, allowing you to make an educated decision as to whether any of them aren't legitimate.
This tool isn't for beginners as it lists every item, not just the suspicious ones. It's up to you to choose which ones to delete, so be careful what you get rid of.
There's a lot of available help in the forums on the manufacturer's website, and fairly detailed documentation within the application itself.