The online virus scanner Housecall, by Trendmicro, now offers a comprehensive scan that includes AV, spyware/adware, and a general security survey. I've had great results with it personally. The only problem with it, is that it requires an active internet connection, and IE with ActiveX. So, this might not work in any case where IE or your internet connection has become corrupted due to said infection.

It's still a beta, and it's still free.