Trusted Information Systems
-- This is one of the few "firewalls"
companies that I'd recommend. Most of them spout seem to spout
nothing but marketing hype. TIS released their
Firewall Toolkit (FWTK) in source form for private and
their licensing agreement). As a result they have the best
credibility in my book. Many people I know buy licenses for their
Gauntlet Firewall -- even if they only use some of the
components from the FWTK.
Another company that distributes a free subset of their commercial
firewall product is SOS Corporation
which appears to have a very liberal license for using the
Freestone subset (or derivative) of their Brimstone