If you are in the area:

Sparky's Garage in Dillon, MT.

Ridgewood Barbecue in Bluff City, TN.

Super Smokers in Eureka, MO (stay away from their other location in Dardenne Prairie)

Arthur Bryant's in Kansas City.

Serious Texas Bar-B-Q, various locations in CO and NM, I've eaten at the one in Durango across the highway from the Super 8.