Most (see reminiscing, below) of the LAN routing I've done used cisco 2600 series, so I haven't really looked for them otherwise.

You could try a different dual Gb firewall with dd-wrt - they seem to have the feature, if not the compatibility with your asus boxes.

If you're not afraid to dig into linux, there are some router packages that run on mini-itx boxes. Never used them, though. Something like this, perhaps, or build your own from parts.

You can roll your own in one of your computers - just put a fiber card in and enable routing.

I'm afraid I can't offer much more help on the hardware side. Perhaps someone else here has an idea.

On topic reminiscing: Back in the dark ages - when big switches were not quite affordable - I inherited an office running on 10bT hubs, "stacked" with 10b2 (coax) links. Damned graphic artists routinely flooded the whole network with large file moves, shutting down everyone. We segmented into four business unit subnets using netware 3 servers as routers. It worked - the artists only annoyed themselves. After a while, the powers-that-be got annoyed enough (both with our and the artists' nagging) to spring for 10/100 stacked switches with a Gb line between floors. Heaven!

-jk