We are fortunate here in Oklahoma to have the Oklahoma Geological Survey. These fine folks present a tremendous amount of material, for free! You will find maps of all kinds, and teaching ideas, and teaching materials. The more time you spend exploring the site the more you will find. I have found it even better to pay them a visit in person – they are on the north side of Norman, east of the airport.
Like most sites, the best place to begin is the tab labeled “outreach”. The link below also takes you directly to a page with lots of geology goodies.
They also have inexpensive materials, like a geology map of Oklahoma that is huge – it takes two bulletins boards in my classroom!