There were so many great suggestions in this thread!

We're back, and we had a great time!

We stayed just out of Keystone, a couple miles from Custer Park. The location was really good, and the campground was really nice. If you want to camp it, but want to have some access to ammenities, Spokane Creek Camp and Cabins is a good choice. Their Cinnamon roles are awesome!

We took in the Mammoth Site, which was actually much cooler than even I thought it was going to be. The fiance loved it.

We drove through both loops of Custer State Park.. Needles and Wildlife. Sylvan lake was beautiful.

We decided to take Trail 9 up to Harney Peak and back. That turned into quite a hike, but I made sure we were pretty well prepared. I would have taken a little more water, as we were out by the time we got back to the truck, but we were fine.

I didn't go into Rushmore, but got some good pictures from several spots. We did go through Crazy Horse. Crazy Horse is much bigger than you would expect, and Rushmore seemed a lot smaller than I thought it would be.

We took the Gas-Lamp tour through Crystal Cave. It was cool, but after 752 steps navigating those tunnels, I was ready to get out. Fiance wasn't a huge fan of the bats, but she did better than a couple others on the tour.

We went though Bear Country, which was really good. They had a lot of animals I don't think we would have ever seen in Custer w/o getting way into the sticks.. (Black Bears, Artic Foxes, Elk etc..)

Keystone is a tourist trap. There's really no other way to describe it. The food was mediocre at best, and too expensive.

We drove up to Deadwood/Lead to see the falls up there, and did a little gambling in Deadwood. We almost got lost on some logging roads north of the falls, glad I had my GPS with me.

Lastly, we did make it down to the Cascade Falls area, and the Angostura Reservoir. The drive was pretty, and the Reservoir was nice, but not sure if it was worth driving all the way back into.