I never use just an antivirus program. I always use internet security programs.. It gives complete protection and no need to install different firewall, anti spam etc. With an internet security you have it all.
I did test 5 different internet security programs over the last 12 months.
Here is my top 3
3rd place - Bitdefender Total Security - good - 8 out of 10
2nd place - Panda Internet Security 2009 - very good 8 ½ out of 10
1st place and in my opinion the best is
ESET Smart Security.- did find infections
the other programs missed - very good 9 out of 10
The other 2 programs I tested, were Kaspersky Internet Security 2009 and
Zone Alarm Security Suite. Both good program, but just not good enough to get in my top 3
I liked ESET that much, that I purchased it and it is now protecting my computer very well.
http://www.eset.com/smartsecurity/
For some extra protection you could install these 2 free very good programs