As a perimeter security gateway and vpn server - for FREE - you can't go wrong with ClearOS.

For my clients, I put 2 solutions together:
*Network Perimeter: Clear OS
*Bullet-Proof Email & File-Sharing, et al: The Zerver
http://solutions.ssiresults.com/zerver.html

I have clients that have been using both of these solutions in tandem for years - and, here's the best part, they never go down. I get support calls on Desktop problems only, never for the servers; set it and forget it. Then, because supporting poor solutions hasn't sapped the clients dry, we can always discuss new purchases to grow and expand.

My Win SBS 2008 clients call me for maintenance on their servers monthly or bi-monthly at a minimum.

WinSBS Server cannot compete with these solutions together.