I like Trend Micro. Simple. Doesn't take up a lot of memory like Norton. Doesn't slow down my pc like Norton. Doesn't mess with other pc settings. Has free online scan that really works. It catches stuff that others miss.
While Norton 360 is probably one of the best commercial offered I would strongly urge you to consider either AVAST or AVG as viable options. Avast and AVG are both free and will provide you the protection you need just fine. You can search either on Google or Yahoo and fine them no problem at all.
Norton 360 Antivirus is number one by a bigshot. It is very easy to use, it's quick and effective. That's what everyone wants isn't it? I've used it for years and have never had a problem with this computer, and 3 years is kinda old for a computer.
I use avast and have never had any problems. Best of all, it's free! I think it's a good idea to have a spyware program too and you can find some good ones that are free.
Avast antivirus is very good and best of all it's free. It has more features than antiviruses you have to pay for. I've been using it for a while. All you have to do is register to get the key. It's free for home use, but commercial use requires payment. Check it out.