There are many specialized anti malware applications, namely:
And so on. What combination of free Windows tools would protect me from any sort of malware?
4 or rather 7 if you are extra paranoid:
If you want to be extra, extra, extra paranoid, throw in:
I couldn't care less about malware, keyloggers and whatnot with this setup.
Depending on how advanced/paranoid you are, when you simply must do something that could potentially harm your PC, don't underestimate the value of virtualization technology. As long as you keep your virtual machines as airtight as possible (no shared folders, etc.) there is little if any worry of your host OS being compromised.
I've used Sun's VirtualBox for this and it is honestly the best anti-malware tool in my arsenal. When your VM is infected (which shouldn't be too often with judicious application of Brain.exe, as pointed out by a previous answer), simply delete the associated hard drive image and start over with a backup one.
Sandboxie, because it is just so much wiser to prevent infections from happening rather than cleaning up when the damage is done (and save your system resources for things that really matter).
Having your computer's network interface removed entirely should do the job. Also don't plug in any external storage devices or disks and make sure to have your RAM cleared regularly along with frequent file shreddings and drive formattings Your files and user experience are now safe as safe can be.
Otherwise Tin-Hat Linux is for you, in all its super safe glory.
Hope this helps, and god-speed