I've heard of a Linux based OS that can fit on a USB stick and has a whole suite of anti-malware/anti-spyware/anti-virus software built in. Anyone remember what that was?
I've got a Windows XP PE install that fits on a USB drive. It's got a few utilities for spyware and malware, but I mostly put diagnostic stuff on it for hardware problems.
Google Bart PE Builder to find a free utility for creating your own bootable BartPE disc and adding whatever utilities you want on it.