1. Spybot Search and Destroy AND
2. Ad-Aware SE Personal Edition (by Lavasoft)
Both can searched for via PCWorld or CNet website or via Google.
Please do run both in tandem as I made the mistake of relying on only one - what one finds the other may not. Keep them updated and run at least once a week.
I had a Malware problem which my AV software did not find and which corrupted my Master Boot Record - running both might have saved me money and grief.....