I second this one. Its a great choice and the home/free version is as good as any subscription based anti-virus I've owned in the past. I also didn't really notice any significant bottlenecks/slowdowns on my laptop after I started using it, unlike my experience with McAfee and Norton.

Most of the other good ones have been mentioned already, Spybot and AdAware do a good job. CCleaner does a great job, especially the registry features which are the real roots of that tool.

I worked a summer position with the government in IT and CA Anti-Virus was great and responsive for us when a worm broke out through the internal email servers. I can't say much about their non-corporate support as I've never tried it though.

Going to throw out another one here while we're talking this stuff. I've been a Symantec Ghost user for many many years, but Acronis True Image is giving it a great run for its money. So if you're looking to backup and make an image of your drive, give it a try!

.dk