Everyone has their favorite but for very small networks that do not have a dedicated IT staff I like:

http://www.networkassociates.com/us/products/mcafee/managed_services/desktop_firewall_asap.htm

If they have a dedicated IT staff then of course checkpoint:

http://www.checkpoint.com/products/firewall-1/index.html
http://www.checkpoint.com/products/perimeter.html
http://www.checkpoint.com/products/safe@office/index.html

For information see:

http://www.cert.org/security-improvement/practices/p054.html
http://www.cert.org/security-improvement/practices/p056.html
http://www.cert.org/security-improvement/practices/p060.html
>Hi all -
>
>I need to install a firewall on an NT 4.0 Server that will eventually be moved up to W2K or higher. Does anyone have a recommendation on a good, inexpensive firewall for my small internal network?
>
>Thanks!