I generally use a combination of Spybot and Ad-aware to root out adware and spyware and I also use Microsoft's tool to catch anything these miss. For the really bad ones that are hard to find, I use HijackThis to read my registry and for the truly evil ones, I use LSPFix to knock out any LSP's that get in my machines.
I'd strongly reccomend you keep HijackThis and LSPFix on your techie disk. They don't actually remove any malware, but they give you the ability to find malware yourself that these other progs may miss.