Black Hills of South Dakota has a lot to offer. From Devils Tower, to the Bad Lands. Days and of great rides and some really awesome attractions and shows. Wife and I went to the Sturgis Rally on 2008. Spent about half an afternoon walking the tents and street venders. Then spent 4 days riding the area. The riding there was great, even with a half million slow H-D riders blocking the roads.
There is so much to do and see. Here is just a small sample.
Devil's Tower area has many good rides out there. You can free climb the tower up to the rubble pile without a permit.
Mt Rushmore is very cool daytime attraction and they have a nice patriotic show at night.
Crazy Horse is another great attraction during the day and they also have a night laser show that is fun.
Custer State Park has the Needles Highway with the Eye of the Needle tunnel. There are several other parks in the area.
Deadwood I think they have casinos.
Jewel Cave Fun in the dark underground.
Bad Lands oddly fun landscape and some interesting roads.