Most people don't have 2 50Mbps providers like Matt does, so most of us don't need fancy hardware to do this. You can install OpenWRT on pretty much any cheap router to do this. (The Linksys WRT54GL is the canonical example).
Having recently needed to replace a router running DD-WRT I discovered that much to my dismay routers that can run *WRT are becoming less and less available. I suppose this isn't too surprising but it did annoy me.
I ended up with a TP-Link access point (one of the challenges was getting an access point rather than a router) and it has so far worked out.
I haven't tried it myself.
http://www.guideband.com/datasheets/EQ-NR-041-guide.pdf