In case you havn't done this yet....
Hell's Half Acre
Hell's Half Acre is a large scarp located about 40 miles (64 km) west of Casper, Wyoming on US 20/26.
Craters of the Moon (Idaho)
Craters of the Moon National Monument and Preserve is a U.S. National Monument and National Preserve in the Snake River Plain in central Idaho. It is along US 20 (concurrent with US 93 & US 26), between the small towns of Arco and Carey, at an average elevation of 5,900 feet (1,800 m) above sea level. The protected area's features are volcanic and represent one of the best-preserved flood basalt areas in the continental United States.
In Yellowstone, if you stop at Old Faithful lodge they will have a list of geyser timing. My favorite geysers are Riverside and Great Fountain. Both are on the lower geyser basin. Riverside is a short walk from the lodge, Great Fountain is a short drive up the west road.
California, Nevada, and Northern Utah are outside my travels. Oh... and Colorado.
Looks like you already have Badlands, Black Hills (Mt Rushmore, and the Crazy Horse memorial), Custer Battlefield, Yellowstone (East Entrance, nice), and the Grand Tetons. We stopped at the rest stop at the Missouri River crossing on 90. It had a great Lewis and Clark museum and some great views of the river and bridge. I always like stopping at the Devils Tower in NE Wyoming. You know, the Close Encounters Devils Tower. Very cool. It does look epic. Have fun.