AVG is terrible. Terrible. Terrible. (Free version)

Microsoft Security Essentials is pretty awesome, and I highly recommend it despite the connotation that comes with it being labeled "Microsoft". NOD32 is also pretty top end, though you have to pay for that.

Just as a note for the OP's list, Avira antivirus has caused one-time disconnects for me whenever it started its automatic update. It was pretty mind-boggling to be disconnecting every night at 11pm until I figured it out.