Malwarebytes' Anti-Malware

Malwarebytes' Anti-Malware is the tool to use if you're looking for something to completely eliminate any of those nasty viruses you might catch while surfing the web. According to its description, it contains "a number of new technologies that are designed to quickly detect, destroy, and prevent malware." While malware prevention is only available in the full version (available for a one-time fee of US$24.95), the free version provides for a virus scanner that puts the vast majority of commercial alternatives to shame.

On a side note: I've recommended this to my own customers rather than the pay-by-month services that failed to protect them.