SUPERAntiSpyware Free Edition
Note: This review addresses v4.0 of the software.
One anti-spyware program isn't enough. This useful program does a thorough job of scanning your system for dangers, and then whacks any it finds. SuperAntiSpyware scans not just your files and memory, but your Registry as well in search of potential dangers. It doesn't offer real-time protection, but it's a worthy addition to your anti-spyware arsenal.