I have one of those Delorme topo maps, but I don't like it.
I know its a lot better then the standard folding maps that you can never get folded back up again, but I found something I like a lot better then both of those.
'The Roads Of Oklahoma' Its made by Shearer publishing.
Its a lot more detailed then Delorme, it zooms in closer (1"=2.5 miles), and what I like most about it, it shows all the back roads in more detail then Delorme. (Paved, gravel, dirt, mud, etc.)
It also shows most major right-of-ways, plus it has history and attractions for that state.
I haven't seen it at Walmart so you might have to order it online.