I was mistaken, the DSL N66U is not able to run custom firmware, at least not Merlin WRT. I'll have to look for this DrTeeth.
Long list of Tomato compatible routers, but I think it has to be something modern, usb port, full gigabit, wan and so forth. Wireless is not a big deal to me, but that's how I tend to find the more popular ones because they all carry faster wireless now as their selling point.