Most of this thread has gone off-topic. Not to say it isn't valid and
justified, it's just not answering your question.
No disrepsect intended to posters...good stuff.
However, back to your question.
If you want to go the route of a SOHO Linksys type firewall router,
one of the perhaps most used is the Linksys WRT54G, WRT54GS. There is
lots of third-party firmware with boat loads of add-on packages. Take
a look at OpenWRT.org, Hyperwrt.org, and http://www.wrt54g.net/ for
more information. OpenWRT is probably the most versitile since it's
position is to start with the core files and add what you need...but
also probably for the more experienced.
In terms of m0n0wall, IMHO, it's the best thing since sliced bread. If
your looking to compare hardware costs, just troll ebay. You can pick
up a perfectly good Dell Optiquest GX110 SFF for under $100. This HW
will beat the pants off a Linksys router coupled with m0n0wall. If you
want to reduce heat and/or a point of failure, put a CF card in place
of the harddrive. You can also pickup reliable Intel or 3com NIC's of
ebay usually dirt cheap.
As for remote office and/or home users, m0n0wall has pptp, ipsec and
if you use a custom image, you can also get openvpn support.
just my 2cents