Oklahoma and Arkansas?

We're heading to Ada, OK in September for a wedding, and will spend a few days seeing Oklahoma, and a few days seeing some of Arkansas. Also will be visiting my niece at Batesville College in Arkansas, but that's about as far east as we can go due to time constraints.

Anyone care to suggest some "can't miss" spots? Would love to hear about good local places to eat - we'd like to get off the beaten path and see some of the other areas.

Thanks in advance!
Kathy