Spybot:
http://download.com.com/3000-8022-10289035.html?tag=lst-0-1
Adaware:
http://www.lavasoftusa.com/software/adaware/
Spyhunter:
http://download.com.com/3000-2144-10209093.html
Spybot is my favorite, but if you have an especially nasty infection, using multiple removal tools is a good idea.