Our all time favorite is the Backstage Magic tour that takes 8 hours and visits 3 of the 4 parks. Second is the Wilderness Trail Segway, and then the Epcot Segway tour. We always try to do "Behind the Seeds" each trip too. I would love to do the Gardens of the World one some day, but haven't done that one yet.
Now in a catagory all by themselves are the safaris!!! We did the Sunrise and Sunset Safaris at AKV this month, and they were spectacular!!!