The Scenic Boat Tour is a big departure from the hustle/bustle theme park world. Very quaint, old Florida ride between the lakes. Sit up front so you don't miss anything that your driver/tour narrator has to say.
The St. Johns River Cruise that TrustedTraveler mentioned is a terrific two-hour nature cruise that goes out into the St. Johns River from Blue Spring State Park up in Orange City - about an hour's drive up I-4 from the Disney area. Well worth doing if you have half a day to devote to the travel, the cruise, and seeing the manatees in the spring waters (in season, about mid-November to early/mid-March for the manatees).
Dick Taylor