You can go with Kaspersky Anti-Virus for Windows Server Enterprise Edition. I am pretty sure it works on Windows 2008 x64 as I have one customer running it on his server.
ESET NOD32 also works on Windows 2008. However I am not sure about x64 build.
Thanks
Rubal Jain // Email - Rubal @ Rubal [dot] Net
Windows Server Setup, Configuration, Troubleshooting, Basic Security & Hardening
DotNetPanel - Helm Control Panel Setup, Installation, Configuration, Troubleshooting
Server setup includes installation of PHP, Perl, Python, ASP.Net Frameworks, SQL Express, MySQL etc and complete integration with control panel.
Authorised DNP Reseller. Get 20% Discount on all DNP Licenses
Authorised SmarterTools, Declude, SimpleDNS (JHSoft), Gene6 FTP, Helicon, Kayako, Icewarp Merak, MailEnable, Deerfield Reseller.