Best Anti Virus for Windows 2003 Std Server

Any recommendations on a Anti Virus for a single Windows 2003 Std Server?

Looking to cover off on Anti Virus, Anti Trojan, Anti Spyware

The machine is behind a NAT firewall; so the basic windows firewall should be enough

I've been using AVG 7.5 on another server; but it looked to be having a few conflicts with windows server services for which I had to manually add a few file excludes to certain dat files related to the services

Thanks

Paul