Linux-based ethernet routers

[Victor Odhner]

I have been looking at info about the Linksys WRT54G which
(if you get the right model) runs on Linux and allows installation
of custom GNU software.  Pretty cool.

But are there any non-wireless boxes that offer this kind of
flexibility?  I'm asking because (1) I'm not interested in wireless,
and (2) maybe somebody who's now into wireless has a
non-wireless router (I need 4 ports) kicking around that
they'd like to get some money for.   :-)

Vic