AdAware's site is
here. It's completely free, and works like a charm! If you run it and SpyBot concurrently, you should stay pretty much ad-free in the future.
For anti-virus I run
Bit Defender . They update the virus defs probably twice a day. It seems to be one of, if not the most up-to-date virus scanners. One caveat though. BitDefender ran like crap on my older hardware. I'd highly recommend it if you're running a P4 or equivalent w/ some decent memory. If you're running an older P3 or K6-2, then look for something else.