I use Avast! which is the same as AVG. I find it very good. I also use spybot-search&destroy which has a realtime checker that lets you know if anything is trying to install itself on your system. If you have enough ram to run it without slowing you up too much then I recommend that.
For more info and a safe place to download stuff from check out
www.download.com . Its always the first place I check
Ben