Lockers are available near the entrance to each park. $7 per day.
Epcot: on the right just past the entrance to Spaceship Earth
MK: under the train station
DAK: Expedition Storage (on the left just past Guest Relations)
MGM: Oscar's Super Sevice (on the right, also stroller/wheelchair shop)
MK and MGM parade routes go past the main entrance, so lockers are close.
DAK parade route is a good 10 minute walk from the locker area.
Epcot has no parade.
Just FYI, there are larger "luggage" lockers available closer to the parking lots (Epcot Bus area, TTC, Bus Info Booth at MGM) if you need to store a suitcase or two on your last day in the parks. Those are a bit more expensive... $12 (???)