I can't give a specific recommendation as I don't currently have a need for gigabit Ethernet or 802.11n speeds, but, I did the dd-wrt thing on a couple of Asus routers over a year ago and I'm happy. They were the 520GC and 520GU models as I recall. Both had external antennae and in the case of the GU it has USB ports on it which I use to share out the home printer.
I'd imagine if you can find a gigabit/802.11n Asus router and a dd-wrt build for it you'd have a solution. Also, I'm pretty sure dd-wrt is well supported on Asus models because, as my brother once said, "I don't think Asus actually expects anybody to use their crappy firmware. Pretty sure they just expect people to put dd-wrt on them." :)