Enterprise level firewall is available from http://www.trustix.org for free

It has such enterprise level features as:
Dynamic Stateful Packet Filtering
VPN support
High Availability
PKI certificate user authentication
Enhanced Traffic Shaping

Full featuer list here:
http://firewall.trustix.com/small/features.html

Firewall has very intuitive WYSIWYG client, unlike any other in the industry - removing most of the complexity related to setting up & managing complex firewall rules

Trustix & Positive Software Corporation are Comodo companies.