The Airport Extreme Base Station is essentially just like every other router in terms of features. So getting any other 802.11n router should pretty much provide essentially the same functionality. The only thing that you might have trouble with is finding a router with a USB port.
I just bought the D-Link DIR-655 and it's a great router. The 802.11n functionality really helps increase speeds and range in my house. Most, if not all, of the dead spots in my house are now gone and the computers that were only getting modest connections under my previous router are now connecting at full speed. It has one more Ethernet port than the Airport Extreme, but its USB port is essentially useless, so I can't stick a hard drive or printer in there like you can with the Airport Extreme. However, if you don't need either of those features, then this is one of the best 802.11n routers currently on the market.
To answer your second question, it looks to be an
Atheros chipset