According to PC Magazine, the best available is "CounterSpy"
The second rated is "SpyBot Search and Destroy" (not Spybot.net: thats a very poor imposter trying to ride of the coat tails of Spybot S&D)

I used to use Spybot, but after installing and trying CounterSpy, I found that there isn't even a close second. First, I ran Spybot S&D. It found quite a few spyware and hijack processes running, and cleaned them off just fine. Then I ran CounterSpy. It found over 20 additional spyware and hijack processes that Spybot missed.

I had done the online update for both prior to running them.

So it seems that CounterSpy is just as PC Magazine claims...by far the best in both detection and removal. The purchased version of Counterspy was around $20.00 when I bought it. They used to have a free trial version, and as far as I know, it's still available for free.

BTW....according to the magazine ratings, the best antivirus program available to date is "Solo". My company tried it out and it did a better job detecting and removing then Norton or McAffe. We completely switched over our network to Solo about six months ago, and we're tickled pink with the performance