i use avast, have done for agies and i swear by it, best Av i have ever used it comes in 2 versions "home" which is free and "proffessional" which charges.
I highly reccommend you check it out : www.avast.com
Im pretty sure kaspersky is. Or Nod32 I think is a little bit worse.
For free virus scanners I have only used AVG Free, and it does an alright job. I have tested it against Nortan, and AVG didn't find any virus, while Nortan found a few and one was actually a trojan. Though some scans may be misleading because they can sometimes consider cookies as adware, or programs you have as viruses even though they aren't.