There is a new, ARM-based board from Banana Pi (BPi-R1) which aims to be used for Routers unlike the devices previously suggested in this thread:
http://www.bananapi.com/index.php/component/content/article?layout=edit&id=59It comes with five gigabit ethernet ports plus an integrated wifi (and antenna plugs) and a connector for sata ssd modules.
Actually, it seems that it only has two NICs (one with a four-port-Hub) yet it might be an interesting, power-efficient option. Too bad m0n0wall seems not to support ARM yet.
FreeBSD/ARM lists the Allwinner A20 on which the BPi-R1 is based, maybe it would be worth a try to build m0n0wall for this target?