We did this in '98. Can't give any recommendations for a company as we booked through Virgin, but it was worth every penny.
We had to get up very early (5am) and it was slightly hazy when we set off. But once the haze lifted and we were in the air the views were superb - we got some excellent views of the Epcot resorts and MGM from the air - albeit from some distance. I don't think they can guarantee that you will get close enough for the views over Disney property, but we were quite lucky.
Definitely worth doing if you get the chance.