Vyatta is a Linux-based router, firewall and VPN solution that can help you affordably build enterprise-class networks by delivering the performance, reliability and features of proprietary networking devices in an open-source package.
Currently Community Version 4(VC4) is in Beta Testing. I’ve Looked at Vyatta before, VC4 is supposed to have large enhancements. It’s also neat that it’s available preinstalled in a VMware(currently only VC3 and VC2.2 as VC4 is not finalized yet).