spybot Search and destroy -
http://www.safer-networking.org/index2.html
Avast Home edition A/v (free and works better than AVG imo) also it doesn't alter your email signature.
http://www.avast.com/eng/avast_4_home.html
http://www.firewallguide.com/software.htm - personal firewall review
Firefox w/ no script, adblock plus, and IE Tab extensions work wonders.
http://www.mozilla.com/en-US/firefox/
Four things I highly recommend. It is amazing how much the last item stops crap from flowing in.