"The BEST option out there, period"4.0 starson by LANjackal
Pros: Fast, easy installation, set-and-forget, highly granular preferences, practically zero system overhead
Cons: Automatically updates virus definitions only, software version updates have to be done manually
Summary: Having used the gamut of security software (McAfee, Norton, Trend Micro, F-Secure, Kapersky, in that order) I'll tell you that it doesn't get much better than NOD32.
Installation is fast and easy. Configuration is extremely granular but logical and easily understandable thanks to the updated GUI. Best of all, NOD is very unobtrusive, keeping notifications to a minimum. The most I've seen is a translucent popup over the system tray when the definitions are updated, and the popup automatically goes away after a couple seconds.
NOD is practically unnoticeable in terms of system overhead, though it will grab and scan downloaded executables and archives, causing a bit of lag in your browser's download manager, but that's excusable. Aside from that, you'll never know it's running.
The only major drawback of NOD that keeps me from giving it a 9 or a perfect 10 is the fact that its autoupdate feature apparently doesn't include versions of the software itself. I find this ridiculous as the subscription is time-based as opposed to version-based like most other security products. For example, I started out on v2.x and upgraded to 3.0 for free, but I had to do it manually. It should be automatic.
But that's my only major complaint. If you run Windows Vista, there's no need for a 3rd party firewall and spyware is already taken care of by Windows Defender, so save yourself some $ and spring for this relatively inexpensive AV product. You'll be glad you did.
BTW I run Vista SP1