For Walt Disney World, I always recommend flying into Orlando International Airport-MCO for complimentary roundtrip transportation to Walt Disney World on Disney's Magical Express;
For Disneyland: there is a fee for Disney's airport transportation.
For Disney Cruise Line: There is a fee for airport transportation. If you fly into Orlando Sanford International Airport (or any other central Florida airport besides Orlando International Airport-MCO) you'll need to rent a car or find private transportation.