specifically, for sport bikes, it's the north west side of arkansas (also the north east side of Oklahoma and the southern side of Missouri).
It's sport bike heaven.
The roads are VERY well maintained, are extremely curvey, well marked, and banked. Not to mention there's MILES of twisties up there and it's BEAUTIFUL.
I have some video from this last trip that I'm going to try and pull off of my camera here in a few.