The Keys to the Kingdom tour is excellent. You'll learn a lot of interesting things, and see some neat backstage areas. I've taken it twice, and both times it was slightly different.
The all day Backstage Magic tour is also fantastic. You visit Epcot, MGM, the Magic Kingdom, Disney Florist, Central Shops (where they work on ride vehicles), and a storage warehouse. You see a ton of interesting things there--like going behind the scenes at the American Adventure, seeing the holiday decorations storage warehouse, going to costuming at MGM to see how the costumes are made, and going into the cast member building at Epcot to see Pride Wall, a hallway that features murals by each attraction or department at Epcot.
Karen