Malwarebytes' Anti-Malware is an anti-malware application that can thoroughly remove even the most advanced malware. It includes a number of features, including a built in protection monitor that blocks malicious processes before they even start.
Avira AntiVir Personal - FREE Antivirus
Protects your computer against dangerous viruses, worms, trojans, and costly dialers.
CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. Additionally it contains a fully featured registry cleaner. But the best part is that it's fast (normally taking less than a second to run) and contains NO Spyware or Adware!
Ad-Aware Free Anti-Malware
Real-time protection against spyware, trojans, rootkits, hijackers, keyloggers, and more!