Broken Bow is nice, don't know about trails there, though.
I found this:
http://www.singletracks.com/php/top....te&state_id=35
At the OK visitor center on Hwy 75, I picked up a brochure, "Oklahoma's Top Rated Trails", which includes a 2-page listing of mountain bike trails.
Seems like they have 2 or 3 cabins you can rent at the top of Palo Duro Canyon.