As a network admin I also suggest OpenBSD as a future platform for m0n0wall.
A GUI or webGUI for OpenBSD is something I have not yet managed to find.
This would also mean using the excellent pf instead of ipfilter, but also
enterprise class reliability and load balancing and also possibly OpenBGPD
for internet routing.
The new FreeBSD 6 still has a lot of work to be done on the IP stack to get
to similar levels with freeBDS 4.x so it may take some time to be ready for