Pest Patrol. I used to use ad-aware. It is very good particularly because it is hard to beat "free", but it just don't catch some things. FastClick and ValueClick kept making comebacks. Their so-called opt-out cookies are totally useless. Pest Patrol, however, is not free like ad-aware but it scans for a lot more and protects you not just from annoying cookies but certain kinds of trojans and bombs also.