I use:

AVG7 Free
Spyware Guard
Spybot Search & Destroy beta 1.4
Spyware Blaster (helps stop Active X installs)
Adaware SE
Microsoft Antispyware beta
Cookie Wall to manage cookies

Run thru the online scanners regularly:

http://housecall.trendmicro.com/
http://www3.ca.com/securityadvisor/virusinfo/scan.aspx
http://www.pandasoftware.com/activescan/
http://security.symantec.com/ssc/vc_...m&plfid=23&pkj
=SDQDZIAZIGAKIYLPMJS
http://www.bitdefender.com/scan/license.php
http://www.pcpitstop.com/freescan/Fr..._EULA_Page.asp

That a few things besides. With all that I still caught a script attack that cratered my machine last week. You can't be too careful these days. The arseholes are twisted, but brilliant sob's.