Brookings:
Nick's Hamburgers. It's a legend that's been in business since 1929. Delicious sliders cooked in molten grease. Not for those concerned about their cholesterol. Great homemade pies.
George's Pizza. Some of the best thin crust/dough I've ever had. Gyros are amazing.
Wooden Legs Brewing. So-so bar food (pizzas and sandwiches) but great, locally brewed beer.
Backyard Grill. There is literally nothing bad here. Ribs, pulled pork, brisket, pulled smoked chicken, etc.
Saké Sushi and Hibachi. Our personal favorite. We get treated like royalty and 9.9 times out of 10 we get free food. Good sushi (for being South Dakota) and noodle dishes.
Sioux Falls:
The one, the only, Sushi Masa. My personal favorite for sushi in SD.
Another vote for Shahi Palace.
Carnival Brazilian Grill. Usually do a birthday celebration here. Eat my weight in grilled meat. Amazing.
Deadwood/Lead:
Sugar Shack. South of Deadwood/Lead on 385. Scary on the outside, scary on the inside. Amazing burgers, great breakfasts.
Montrose:
Special mention to the "Irish Pub". Got a motorcycle route that takes me through Montrose. Great place to stop for a break, beer, and burger and fries. Reminds me of a place that should be out at the lake (Poinsett, Oakwood, etc.).
Oacoma:
Al's Oasis. How could anyone forget Al's? Buffalo burgers, homemade pies.