The Dr Pepper museum is located in Waco, Texas, USA, and manages to be a real museum and not just a glorified gift shop/tourist trap. They have a few interactive exhibits, but just looking at all the cool stuff and reading the interesting bits of history is the best part. That, and finally being able to buy that bottle of Imperial cane sugar Dr Pepper (which you would think would be available in the soda fountain or at least chilled, but it's not). Most of the urban legends about Dr P are addressed, as well as pressing questions like where the period in "Dr." went. The gift shop is good too, I picked up a nifty pen and some other things--and should have bought the Dr Pepper cookbook for my cool mom.
This is the Mecca of real Dr Pepper fanatics! Don't go to central Texas and not go there, lest ye be doomed to an eternity of flat Coke in punishment. It's easy to find in downtown Waco, just follow the signs. Admission is low, plus there is a student discount, and you can find a coupon in the local tour guide. I'll add some more information once I find my newsletter, or the http://www.drpeppermuseum.org/ website is operational again.