Several ideas, based on where you are staying. Going via boat for any location is wonderful at night.
If close to Downtown Disney, boat from PO, dine at Portobello Yacht Club, then catch the first comedy show at the Comedy Warehouse, then jump to The Adventurer's Club for the best fun at WDW.
Or try Boardwalk. Dine at Flying Fish then stake out a table at Jellyrolls for really fun dueling pianos, or take the boat back in to Epcot, get a glass of wine and watch the fireworks from France.
Dinner at upstairs France, Bistro de Paris is very romantic, then stroll Epcot and enjoy the "adult" things, like watching the sugar sculpture in Japan and riding Fast Track until you're sick.
Or, get the first seating by a window at California Grill then take the monorail or boat to Magic Kingdom if it is open late and just stroll around and watch the fireworks, boat back and get dessert at the Grand Floridian.
Or boat from Boardwalk or Swolphin to MGM, eat at the Brown Derby and see Indiana Jones at night. Stroll back on the lighted path.
We've done them all, and loved each one.
Carla