I would actually suggest Norton 2010, if you can spare a bit of change, because it's probably quite good.
I used to use Norton 2009, and it was great. Didn't use that many resources, wasn't intrusive, etc. It was just all around great; 2010 is supposed to be even better.
That being said, I'm using Avast and the default Windows Firewall right now, because I don't want to pay for something that really isn't a problem here. From what I can tell, I haven't really had any viruses or anything. Heck, Avast hasn't detected a single thing for me... like... ever. Either the viruses I have right now don't do anything at all (and Avast isn't picking them up...), or I'm just not being enough of an idiot for it to actually do something.
Oh, and Avast is pretty good. It kind of stays out of your hair...
... Maybe a little too much. Sometimes I don't know if it's actually doing something besides detecting a random false positive every now and then. The only thing it does these days is pop up that little blue notice up and go "Your virus database has been updated". >_>;