Don't use Norton... slows your PC down too much.
I used ESET for 2 years and I did not had nay problems with it at all. Always detected a threat on a website and it did not slow my PC down as much as Norton did.
I recently got AVG for free when got my PC built.. .seemed cool but It didn't protect my computer properly and got *** lots of Trojans and had to reinstall my system 2 days ago.
I be getting Kaspersky Internet security tomorow from my local shop for £20 (official website price is £40)...
Kaspersky seems really good considering the reviews and I will give it a go.
Reviews on the best AV : http://anti-virus-software-review.toptenreviews.com/v2/
Also some might suggest free AV software... Its your choice but knowing that you pay a company to build a software which gets good reviews is the best way to be sure that you are well protected. But thats just me....