Avast Antivirus and Emsisoft Anti-Malware both work great on Windows 7.

I had a problem where my computer wasn't installing the Windows 7 updates for a while. Then I discovered that the TrustedInstaller service was missing. After I got that installed properly my computer now updates properly. It took me over a month of trying different things to finally figure that out though. Just a tip for anyone else that can't install their Windows updates.