I've been more or less happy with Symantec Corp's Multi-point protection. It included coverage for the workstations and also the exchange server including anti-virus and anti-spam (very effective anti-spam)
Down side is the workstation anti-virus clients are becoming somewhat bloated, so if you have really old workstations or not much memory in them you'll notice they will seem slower. But it runs great on our newer ones, and we only get low end Dell's with 1 gig of ram.
You can even push out the installation of the client using Symatec's own deployment tool from the server. Worked great so you can completely control it from one server. Your subscription includes the defination updates for all clients, the mail server and phone support for a year.
They have some pretty good volume discounts as well.
Sorry I miss read the part where you said you didn't want commerical products, I thought it said those were ok to. That said, if you don't find anything in the open source (I never did that met those needs) you might still want to consider it.