This past week, I installed a Windows Home Server for my grandmother. One of the pieces of software that I wanted to install was an anti-virus program for the server, and all of the computers in the house. I chose the avast! Professional Family Pack, which includes the avast! Windows Home Server Edition and a 10 pack of avast! Profession Edition client versions, Avast! really seemed to work well for her install.
This post has a review of the home server version of avast!.