Spybot
System Security Suite
CCleaner
Be careful with the last if you use an ipod - it seems to move the music to odd places, maybe back it up first? For me it gets rid of loads of, well as the full name says, crap!
I find reading the IT supplement of the Guardian on a Thursday tips me off about good programs.
Also - anyone else found HiJack That or something similar useful? You use it and then post on a geeks site and some kind nerd helps you clear unwanted stuff off your pc! I'll have to track it down again...