Deadwood, SD does have gambling. I believe Kevin Costner, the actor, had a hand in some gambling development. You will most likely pass through Deadwood when going from the Black Hills to the Devil’s Tower or vice versa.
At the rate they are going, the Crazy Horse Monument will probably never get finished. You do start to see some of its form and it is considerably larger than Mt. Rushmore. When you do go to Mt. Rushmore try to be there in the evening when they have the lighting ceremony. Also, tune up by watching the DVD movie North by Northwest with Cary Grant and the Mt. Rushmore climactic ending.
The Bison roam free in Custer SP. You can get awfully close to them, too close maybe. Wind Cave NP nearby is an easy short underground cave tour.
Sioux Falls, SD is on the border with Minnesota at the eastern end of the state. A long boring trip just for one road food stop. [;)] But if you do make that leg, which I doubt, you have to check out the Corn Palace in Mitchell, SD. [:D]
If you go to Glacier NP check out the two grand lodges. We stayed at the Many Glaciers one. Also if you can take a trip up to Waterton Lakes NP in Canada bordering Glacier. It is an interesting contrast. The grand lodge at Yellowstone’s Old Faithful geyser is also a must see.