Panda online software has an online scanner which I find to be very good as well.
The best way to keep a computer spyware clean of course, is to be careful when downloading programs and archive files and try to avoid websites which plant drive-by spyware. IE Spyads is a good program for this, and will add hundreds of websites to your restricted zone for you. I use layered protection - AVG for viruses, Adaware, Spybot, and Panda for spyware that's already there, and spywareblaster and spywareguard to prevent infections in the first place (Spybot also helps with this).
Here is a site with programs to prevent and combat spyware - and many of them are free. I have used my combination of them to keep my computer spyware-clean for at least a year and a half.
http://www.spychecker.com/