Another vote for AVG here, been using it for over 6 years now and never any problems.
HATE Norton, had to help a load of friends who cant get it off their computers. i mean, if you dont want norton on your machine, you just uninstall it, right! WRONG! after messing about for ages, you then find out that if you do want to uninstall, you have to download and run a norton removal tool from the norton website. Why they have to make it so difficult for us to get their software off our machines, when we have to shell out a £30 subscription a year to them for it in the 1st place. hmm.