I support over 1000 desktops across the country for our company.

Corporate-wide we use ESET for antivirus, but I use Microsoft Security Essentials at home. I am a low risk user, as I am familiar with the social engineering methods used to push malware.

For spyware removal, I use both Malwarebytes.org and superantispyware.com.

IE can be tweaked to automatically clear temp files on exit, it's in the Tools-Advanced menu. This helps a great deal.

In addition to keeping a dedicated administrator account for install and cleanup purposes, it's a good idea to boot to Safe Mode before scanning with many utilities, as it is less likely that malware services and processes will start at boot. Safe mode is accessed by pressing F8 as the computer first starts.