Kaspersky is the best I've tried yet. You have to customise it a little but its safer and better than any of the other Fee paying AVs around. Avira is my freebie choice though again if it's slowing you down you'll need to customise it a bit.
I second saran008's second opion. Why not give Microsoft Security Essentials a try? It is a free download (so you don't have anything to lose) and seems to be a favorite of many. If you're still on the hunt and want to learn more, visit http://www.microsoft.com/security_essentials/