Jumping in to say the closest road, right outside the airport. is the Beachline (formerly Beeline) Expressway. There are 2 or 3 tolls you go through before reaching I-4, which takes you to Disney.
Also, Florida toll roads don't subscribe to EZPass, which is found from Maine to at least Maryland. They have their own system, Sunpass I think. If you have EZPass like we do, it can't be used on the Florida toll roads so have your dollars and quarters ready.