When I researched before my last trip to WDW I found that almost all pictures were taken from 18mm to 40mm. After making my trip down there I found this to be very accurate. You will need a wide angle and faster lens for inside and after dark MUCH MORE than you will need anything long. You can check out my gallery of WDW pictures HERE. These were taken with my D7000 and a Sigma 17 to 50mm F2.8 lens. You might consider just renting a lens for ths trip instead of purchasing anything.
I might add that I now own a D600 full frame camera and will be taking one lens with me when I go back to WDW this Thanksgiving and it will be the equivalent lens for the D600 which will be the Tamron 24-70 F2.8.
On any pictures in my gallery that you want to know the EXF data just put your pointer towards the top right hand side of the bigger picture to the right and click on the little blue box with the "I" for info in it and you can see what each one was shot at.
Thanks Grandpaw!
Now you got me wanting the Sigma 17-50mm f/2.8!