Thanks to everyone for the great feedback. Very helpful!
Sounds like m0n0wall will be more than capable of meeting our needs,
provided the hardware is adequate. We have a nonsaturated T1, so the
Soekris 4801 might just do the trick. If we do go with the 4801, we may see
if it can handle a little traffic shaping without hosing the webGUI. If
worse comes to worse and it does hose the webGUI, we can probably get by
without any shaping, as we're not doing any currently.