In an earlier post I speculated that the CherryPal PC might be a possible option for users considering replacements for the slug. But that device has still yet to hit the streets and is beginning to look suspiciously like vapourware. However, linuxdevices, the site devoted to linux on embedded devices, wrote about the interesting looking french made linutop some months back. The linutop site looks to me as if it is actually taking orders.
Now if they could just ship one with two ethernet ports, it might make a good base for a firewall.