Although I personally hate these kinds of programs (they do more damage to the computer than the virus, as they slow it down - just my opinion!), my father runs Kaspersky on his machine. In my opinion, it's the best.
Kaspersky seems very popular as well in general. Avoid Norton like the plague - that really is a performance killer, and from my experience it misses a lot of stuff (I recommended my father to get Kaspersky and get rid of norton). NOD32 is also worth a look into, although I'm not sure that comes with a firewall.
But yeah, Kaspersky is the best in my opinion. Just up the "scan level" to high otherwise it misses stuff (I was getting fed up of Kaspersky as it wasn't finding a virus I knew was on the machine - until I upped the setting). Kaspersky isn't too much of a performance hog either (you'll notice it, but it won't make your computer unusable like norton does). Read reviews on the net and you'll find Kaspersky is the most popular.