Spyware doctor is pretty good, depends what type of virus you have, trojan, spyware etc and whether you are already infected or not. Sometimes you're better off just buying the software
I use Microsoft Security Essentials and a program called Threat Fire which is a not so much a virus scanner as a suspicious activity monitor - it supposedly increases your protection by offering a line of defence against 'new' virues that may not have been written into your anti visus' definitions yet.
I supplement all that with weekly scans using Malwarebytes Anti-Malware.
All are free and avaialbel from either the MS website or Download.com
AVG is regarded by many as being the best. however their detect rates have been dropping and people are starting to move away from them.
Avast! is good because it doesn't just rely on the definitions and is able to detect a virus before it becomes known.
Security Essentials is very user-friendly
Panda doesn't slow your computer down when scanning.
there's no really much between them - comes down to personal preference.
Spybot Search & Destroy. Routes out and deletes things before they become a problem, rather than usual anti-viruses that just fix a problem when it happens.
Comments
I use Microsoft Essentials:
http://www.microsoft.com/security_essentials/
I supplement all that with weekly scans using Malwarebytes Anti-Malware.
All are free and avaialbel from either the MS website or Download.com
AVG free - http://free.avg.com/gb-en/download-avg-anti-virus-free
panda - http://www.pandasecurity.com/uk/homeusers/downloads/
avast! - http://www.avast.com/free-antivirus-download
Security Essentials - http://www.microsoft.com/security_essentials/
AVG is regarded by many as being the best. however their detect rates have been dropping and people are starting to move away from them.
Avast! is good because it doesn't just rely on the definitions and is able to detect a virus before it becomes known.
Security Essentials is very user-friendly
Panda doesn't slow your computer down when scanning.
there's no really much between them - comes down to personal preference.