A good compliment to Stu's sticky here:
http://www.cableforum.co.uk/board/showthread.php?t=6152
Obviously, if you're in the market for an anti-spyware tool, you don't need to look further than Stuarts thread, however...
For those that like to tamper and test ( who know who you are
), here is a great guide to the ones you should avoid:
http://www.spywarewarrior.com/rogue_anti-spyware.htm