As others have said, good rolling hills in the rural areas east of OKC and Edmond, especially in the area near the little town of Jones. Numerous loops from there to choose from. But they're not all hilly, there are flat loops to choose from also.
Most of the groups departing for Jones from Oakdale School are informal group rides and open to riders that ask to join.
If you're going to be near Tenkiller and you want some hills, you might consider going on up to the dam at the south end of Fort Gibson Lake. There's some mile long climbs there and a 19.2% grade near Sugar Mountain that will test you. I did a 50 mile loop there last weekend.
I guess our best hilly region is Talimena Drive in southeastern OK. Years ago, Car and Driver magazine identified it as one of the top 10 sports car roads in the US. The blacktop (State Highway 1) runs along the top of the mountain ridge line for 60 miles to Mena, AR. There is a loop called the Talimena Triple that has about 8000 ft of climbing over an 80 mile loop. You may want to swap out your cassette before venturing down there.
In OKC There's a MUP that provides about 25 miles of traffic free riding along both sides of the river that runs downtown. It's kinda new so there is VERY little traffic on it - you can even hammer it if you want. There are two lakes in town with road/MUP combos, that although crowded, are still very popular.
Plenty to choose from.
I'd be happy to email some route maps if you're interested.
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