BitDefender, Kapersky, and NOD32 have consistantly been at the top of AV-Comparatives.org for over a year now. Kapersky was historically "heavy"...but their recent version really lightened up. Has practically hourly updates. NOD32 was always known for being very light, usually has several updates a day.
These 3 are not only good at getting viruses and worms, but also quite a bit of the ad/spyware trojans out there too.
For ad/spyware tools, I carry these on my USB thumb drive "bag of tricks" for working on PCs. Spybot Search and Destroy is one of the long time favorites. Update and immunize frequently for some prevention, decent detection/removal rates. I don't use the teatimer real time protection though...it's naggy. I always install it as part of my standard setup.
Adaware is another removal tool, freebie version has no prevention. Update and scan/remove...decent job at it.
SpywareBlaster is a freebie prevention tool...not a removal tool. Protects Internet Explorer, as well as Firefox. Think of it as a "condom for your web browser". Update definitions every now and then.
Ewido is a removal tool, they have a free trial version, I use this on some infected PCs. One of the better ones are removal.
SpySweeper, from Webroot, is one of the better ones. I'm not sure if they still have their free trial anymore.
And....even though the name sounds stupid...there's a relative newcomer to the scene...SUPERAntispyware. It's free...and has very good detection and removal...I've been using it for a few weeks now, even after using all the ones listed above...it's found quite a bit and done a decent job...even getting lots of stuff from SpySheriff/SpyAxe/Smitfraud family. I HIGHLY encourage all techs here to add this one to their USB drives.
Microsofts tool..back when it was Antispyware from Giant...I loved it. Decent at removal, but more importantly, the Advanced Tools were very usefull, allowing you to peel into the BHOs and winsock...but when they moved it to Windows Defender..they took that away. And it's detection/removal rates have plummeted.