Best Diagnostic / Spyware Tools

Guys,

I try to help a lot of friends and even do a little side-line work working on PC's after the fact that the person doesn't have anti-virus, spyware, or any kind of protection and then traverses the Internet picking up all kinds of nasty items that in effect make Windows of any type a mess. Even using tools such as PCTools Spyware Doctor, System Mechanic, and lots of others I've found that do a good job - Windows usually remains pretty screwed up. Is it best just to back up pertinent data and reinstall / run recovery partition (if one) to bring it back to original state or are there better Administrator products out there to use.