promixitron.org - blocks popups and is free and configurable.
grisoft.com - free antivirus with frequent updates. I removed 73 instances of virus from a friend's computer with this thing, after her norton's liveupdate subscription had expired.

Spybot - I haven't tried this personally, but several techheads I know swear by it, and say there's frequent updates. Since ad-aware wasn't updated for quite a while (almost a year) it would be better to get spybot right now. It warns you of any programs that try to send out information about your computer, and you can then delete the programs. Useful. Get it - I'm getting it soon.

Firewall - it's a really good idea to get one of these too. Right now I'm behind a router's firewall, so I'm somewhat ok. I'd add a software one for the best protection, too.