Vipre Antivirus is apparently pretty good, because it is rated pretty highly by both download.com and majorgeeks.com.
Vipre is made by Sunbelt Software, who has a good reputation and has been around computer security for quite a while.
BUT if I were to ever use a paid antivirus (*), it would be ESET NOD32 (or the full security suite, ESET Smart Security.)
(*) I use and recommend the free version of Avast.
> Avast Free v6: http://www.avast.com/free-antivirus-download
on: 22nd April 11