Try
Super Anti Spyware. It's free. I run this along with my AV, and it will occasionally pick up something that's been missed.
Another thing I like is
Iolo System Mechanic. It does a lot of maintenance that I don't have time for, or don't know how to do. My desktops have run better/faster since I started using it. They don't crash, which is surprising with me pushing buttons.