Epcot = The Store in the Japan Pavilion is pretty neat, probably more so if you have kids, but my fav is the Yong Feng Shangdian shop in China, has beautiful carved (expensive) pieces of art.
MK = My parents bought my brother and I toy rifles at the Pirate's Bazaar store so it will always remain my fav.
MGM = Hands down The Beverly Sunset store for it's villains stuff.
AK = dunno, never shop there, just roam.
DTD = Reel Finds, you can spend an hour just taking in all the memorabilia in this small store.