I recently downloaded Microsoft's newest AntiSpyware beta release. As spyware-fighting software goes, it has a great advantage: it's free. Once installed, which in the case of Microsoft means I merely had to sign away all rights and first born child, I was ready to give it a try.
Running the scan on my trustly old 20 GB Dell took about 20 minutes. The program detected several suspicious items, including trojans and several adware items. It then offered to remove, isolate or ignore each one. I selected an action for each item and clicked Continue. Antispyware cleaned up my system and then rebooted.
Word-of-mouth says that it's a better remedy than a preventative. Some people have reported that won't stop spyware from installing, but from what I've seen it's pretty good at getting rid of the stuff that's already there.
AntiSpyware [Microsoft]