There's Mount Rushmore, of course:
And Crazy Horse (I hope they finish this -- it will be spectacular):
We also took a tour through Jewel cave, the 2nd largest underground cave in the world. We went on the "scenic tour" but for the more adventurous there's a 4-hour tour that involves crawling through some pretty tight spaces.
Now no trip would be complete without a yarn store sighting -- and I was happy when I spotted the following place as we were about to start the long journey home (unfortunately there was more 'stuff' than 'wool' - boo!):
All in all it was an excellent trip.