Modem
Motorola SB5101U
Router
D-Link DIR-615
I've had the router for awhile, no problems with it that I can recall. Even though it's wireless, I go wired for the Xbox. I've had the modem for a couple months, and haven't had a problem with it either.
I don't know if Comcast fucked up (or did it on purpose), or if it's the modem/router combo, but we pay for 12 Mbps and regularly get anywhere from 16 to 20 Mbps.