1. AVG Free Edition
2. Avast! Home Edition
3. BitDefender Free Edition
4. ClamWin

AVG Free Edition

Very well known by many users and you could be one of its 80 millions users. This is free for non-commercial use.

Features highlight

• Automatic Update
• Email Scanning
• On-demand scanning

Avast! Home Edition

Light and easy to use/update. Download size is approximately 28 MB. It is free for home and non-commercial use.

Features highlight

• Resident shield and self-protection
• Free Automatic updates
• Web and P2P protection
• Anti-spyware & anti-rootkit tool
• Over 30 language versions

BitDefender Free Edition

An on-demand virus scanner, which is best used in a system recovery or forensics role.

Features highlight

• Virus scanning and removal
• Scheduled scanning
• Immediate scanning
• Skinable interface
• Quarantine
• Reports

ClamWin

A Free Antivirus program for Microsoft Windows 98/Me/2000/XP/2003 and Vista.
Very light and easy to use. It comes with an easy installer and open source code.

Features highlight

• High detection rates for viruses and spyware
• Scanning Scheduler
• Automatic downloads of regularly updated Virus Database
• Standalone virus scanner and right-click menu integration to Microsoft Windows Explorer
• Addin to Microsoft Outlook to remove virus-infected attachments automatically

There’s also a portable version (created by portableapps.com) which you can run it from your USB disk on any computer running Microsoft Windows.

Recommendation

From my experience, I’d recommend Avast! Home Edition. It’s light, fast, seamlessly daily update, no ads, detect most current known virus.

If you prefer a paid or commercial version (normally comes with user support), I’d recommend BitDefender. It’s best value for money, I find it the cheapest for performance and feature for Internet Security Software.