Kaspersky Anti-Virus 2013 13.0.1.4190 / 2014 14.0.0.4417 Beta

An antivirus that provides all types of anti-malware protection
Developer: Kaspersky 
License: Trial
Size: 147 MB
OS: Windows 2K / XP / Vista / 7

AVG Free Edition 2013 Build 3343a6324

The world's most downloaded free security software
Developer: AVG Technologies
License: Ad-supported / Free
Size: 130 MB
OS: Windows XP / Vista / XP X64 / Vista64 / 7 / 7 x64

Avira Free Antivirus 13.0.0.3640

Extensive virus protection for home users
Developer: Avira GmbH
License: Ad-supported / Free
Size: 2 MB
OS: Windows XP / Vista / XP X64 / Vista64 / 7 / 7 x64

Avast! Free Antivirus 8.0.1489

Reliable antivirus software with spyware protection
Developer: AVAST Software
License: Ad-supported / Free
Size: 112 MB
OS: Windows 2K / XP / Vista / XP X64 / Vista64 / 7 / 7 x64 / 8 32-bit / 8 64-bit