The 3 below are a good combination:
http://www.spybot.info/en/index.html
Spybot Search & Destroy 1.6 is a very good, FREE Anti-Spyware Program.
Download, install, update, and immunize your System with it.
Then SCAN with it.
Update it, and scan your System once a fortnight.
http://www.javacoolsoftware.com/spywareblaster.html
SpywareBlaster 4.1 is a non-intrusive, FREE Anti-Spyware Program (no
scanning by you!).
SpywareBlaster prevents the installation of many so-called spyware, adware
and malware programs by disabling the CLSIDs of popular spyware ActiveX
controls, and also prevents the installation of any of them via a webpage
Update it once a fortnight.
http://www.malwarebytes.org/mbam.php
Malwarebytes is as the name says, a Malware Remover!
For the Free version scroll down their page to either download from
Download.com, or Major Geeks.com
Download, install, and update.