i also have a couple of av's
as well as spybot,adaware, and cwshredder.
i beleive untill i have problems i feel secure.
You can have as many as AVs you want, but only have ONE running in the background.

Rather than buying a AV product from a company, why not search there website too see if they have a free online scanner?

Online scanners-
Trend Micro (housecall):
http://housecall.trendmicro.com/

Trojan scan:
http://trojanscan.com/

BitDefender:
http://www.bitdefender.com/scan/licence.php

Panda Activescan:
http://www.pandasoftware.com/activescan/

There are alot more.