We went to South Dakota and had a lot of fun. We were heading home from Billings Montana then on to Sioux City then turned South.
We stayed the night in Custer across the street from the Flintstones amusement park.
Here's a map of where it is from Mount Rushmore. This map also shows the main highways to around the variety of monuments.
http://www.flintstonesbedrockcity.com/where.html
We didn't stop and pay to go to the monuments, we had seen all the shows on the History Channel. It was still very fun to see, even if it was from the highway. We came up to Mount Rushmore from the back at first. I have looked at aerial maps and cannot figure out what we did but we came up on Mt Rushmore on our left. We parked and walked around and could see it from a lookout point. There were white mountain goats everywhere and interesting rocks. We left that area and then drove around to the main entrance and the little pull off area on highway 244.
Crazy Horse is pretty awe inspiring. I enjoyed it more than the other things we saw. Maybe because it is a work in progress.
We had a lot of fun going to Wall South Dakota. It's a tourist trap for sure but the food and break from driving is quite refreshing. The signs are fun to watch for and the kids really enjoyed it.
We really enjoyed the Badlands, their beauty and roughness really made me think about the Western days and how they lived as outlaws.
Further East is the Corn Palace, it is very interesting. If you go during Summer you can go inside and see the way they make everything. The tourism books will have a lot of road trips and other attractions you can see.
Here are some websites that have different aspects of South Dakota.
http://www.blackhillsbadlands.com/home/planyourtrip/maps/...
http://www.bing.com/maps/default.aspx?v=2&cp=43.87882...