I second the idea of the Lake Angostura area at the south end of the Black Hills. Didn't camp there, but we had a lovely time visiting there.
Voyageurs is pretty remote, and I am not too familiar with the actual Voyaguers area because we don't usually go quite that far north and haven't been there, but this place is right on Lake Kabetogama about a mile from the Voyageurs Visitor Center. It looks like a nice place, though a little on the spendy side...
Pines of KabetogamaYou could also take a look at this place:
Voyageurs Sunrise ResortWe stayed two nights at the Medora Campground when we visited TRNP. It's OK. A little tight and packed in. Our site had a beautiful view of the ridge. I don't think we were able to put out our awning. Sites are packed dirt so could be really muddy if it rained (we were lucky...) Suprisingly enough, there isn't much for campgrounds in that immediate area.
