Malwarebytes Anti-Malware is a surprisingly effective freeware antimalware tool. It's a relatively speedy malware remover, with the quick scan taking about 8 minutes even with other high-resource programs running. The heuristics engine proved on multiple computers during empirical testing that it was capable of determining the difference between false positives and dangerous applications.
The app has some nice features rolled in, too. It supports multiple drive scanning including networked drives, context menu options including a scan-on-demand for individual files, and the FileAssassin option under the More Tools section for removing locked files. The interface is simple, but pleasant-looking and well-organized.
Malwarebytes' Anti-Malware is a high performance anti-malware application that thoroughly removes even the most advanced malware and spyware.