Webroot's SpySweeper is a great one, but you have to pay $29.95 a year after a 30 day trial period.
Spybot Search and Destroy is a good free one, but you have to use their tea timer to prevent things from installing themselves in your registry...but it's also free.
I personally run SpySweeper and Spybot Search and Destroy. I am trying out Microsoft's new spyware killer...so far it's not too bad.
Hope this helps.
ping