i recommend nod32. i haven't really found another antivirus problem that uses less resources. the scans are pretty fast. if i didn't use nod32, i would use kaspersky. it has the highest rate of detection (in a full deep system scan), but it uses more resources. the old version 5.0 used to add its own annoying extension to every file that it scanned, which was really annoying. i think that the newest version scans a lot faster and has a smaller footprint, so it's comparable to nod32. nod32 is the fastest and smallest that i've found, though.
stay away from norton though. system resource hog, and mediocre detection rates. my school uses the corporate version of symantec, and it barely protects against anything. pain in the butt to use.
if you're not willing to pay for antivirus, try antivir or avg. those seem to be the most popular. there's also clamav, but i don't know how that is. i think a while ago, aol used to offer kaspersky without the active protection, and they called it activevirusshield. i just checked, they don't offer that anymore.
in the past, i've just run zonealarm under an account with no administrator privileges w/ firefox + some plugins for that without using any antivirus. that's served me fine for several years. just use your common sense, and you'll be able to avoid anything nasty. (immunize your system with spybot + spywareblaster. doesn't use any resources at all)
of course, if you're truly a minimalist, just use linux.
Ubuntu Home Page | Ubuntu no viruses there. haha... (
List of Linux computer viruses and worms - Wikipedia, the free encyclopedia)