Free Anti-Virus

a-squared
a-squared is a completely free AntiVirus package for private use.
It can remove spyware,malvare,Trojans, Backdoors, Worms, Dialers, Keyloggers etc.
Download page is here.
-------------------------------------------------------------------------------------

Avira AntiVir®
Free virus protection for Windows and Linux/FreeBSD/Solaris systems.
They are maintaining a virus definitions page here
Download page
-------------------------------------------------------------------------------------

Avast Home Edition
Avast Home Edition is a complete Checkmark certified antivirus.
It has on access scanner, e-mail protection,Network traffic--intrusion detection, lightweight firewall, P2P protection for Kazaa, BitTorrent etc.
Download.com link
-------------------------------------------------------------------------------------

AVG Anti-Virus Free Edition
AVG Free is the free solution available at no cost to home and non commercial users and provides the high level of detection capability.
No Technical support for the Free Edition.
Download
-------------------------------------------------------------------------------------

BitDefender Free Edition
Bitdefender allows you to enjoy basic virus protection for free.
It is a Windows only software.
Features include on demand scanning,immediate scanning and quarantine etc.
You must give your email id to receive a download link.
-------------------------------------------------------------------------------------

ClamWin
ClamWin is a opensource Free Antivirus for Microsoft Windows platform.
You need to manually scan a file in order to detect a virus or spyware.
Download Page