Where are you coming to the Badlands from? I'm guessing that you will have already seen Mt. Rushmore, Devils Tower and Custer State Park. A couple of the tourist traps in the area are Wall Drug and the Crazy Horse carving.
See if there is something you want to see in Sioux Falls SD.

Thanks! Not planning to get to Wyoming unfortunately. We will go to Mt.Rushmore and Custer State park and arrive at Badlands from there.

Sioux Falls is a possibility.

It looks like you'll be taking Interstate 90. You could see the large statue of the Jolly Green Giant in Blue Earth, MN. There's a tour/museum in town on certain days too. The Spam Museum in Austin, MN is a hoot. Free samples too. Also in Austin is a little diner that was voted one of the top 100 burgers in MN. This one a loose meat sandwich I can find that name if interested.

The Amish are a fun study in SE MN. There are tours too, but we just drive through the countyside. Forestville/Mystery Cave is interesting.

Lanesboro, MN has cute shops and it quite the trendy town for southern MN. Lots of wineries along that MN/WI route. Will you have kids along?

Not much happening in Souis Falls, but the falls are quaint.

No kids, just us adults at the end of a road trip heading back to DC. We really want to break up the driving into shorter chunks of time. Souix Falls was the best we could come up with as a stopping point, but looking for other ideas.
Great ideas! Just what we are looking for. The Spam museum is a not to miss 4 us.
@Googs - I think I have been commenting on your thread about coming to DC?

Yes indeed, D.c., thank you for all your help there.

Souis Falls will have the most selection of hotels in the area you're traveling. Austin is a sleepy town, but we drove down last fall with the mission of going to the Spam Museum. Amazing all that's inside. We stayed at the Holiday Inn Conference Center which was dated, but the biggest hotel in Austin. Tendermaid is the loose meat sandwich place. Greasy-good with stool seating. http://www.minnesotamonthly.com/media/Minnesota-Monthly/July-2008/Burger-Kings/

What month are you traveling?

La Crosse, WI may be a good stopping point. Mississippi River has many points of interest. Last summer we stayed at the very nice Grandstay Residential Suites in La Crosse, WI. This is walking distance to the river and lots of summer activity.

We'll b traveling mid July. We're thinking of making one stop in Madison Wis and driving to Chicago from there. So looking for places between Badlands and Madison. But completely flexible. I'll look at La Crosse, WI

I'm not sure how far you want to stray from your southern mn path to Madison, but Red Wing, MN is appealing. We stayed there new years eve and had a blast. A bit touristy with it being the home of Red Wing Shoes and Red Wing Pottery, but there's many grand antique places, historic homes and trains. One large antique place has a restaurants and holds the pottery museum in it.

While there we also visited Falconer Vineyards and had the most esquisite time, especially getting a tour from Mr. Falconer himself. If you're there in the summer the place would be breathtaking with the large deck overlooking the vineyard.

South of Red Wing is Wabasha, home of the movie set Grumpy Old Men. The National Eagle Center was fun for us. Hadn't seen eagles so close (five live there). These two cities are along the Mississippi, so Picturesque.