Wander around Adventureland! I love it there at night. We like to ride the Jungle Cruise and Aladdin at night, and grab a dole whip! I also like going to Frontierland and riding BTMRR and Splash at night. If you wait late enough, these usually don't have much of a wait.
Definitely rail road, Peoplemover, and Jungle Cruise in the dark. Storybook Circus looks cool with the lights. There's a nice view of Cinderella's Castle, Beast's Castle, and Space Mountain all lit up from the courtyard in front of Gaston's and in front of Little Mermaid. Main Street has beautiful lighting at night.
I love the Carousel at night. Not very exciting, I know, but there is just something about being on that beautiful old carousel near the castle, in the middle of Fantasyland with everything lit up.
Hall of Presidents, TTA, Philharmagic, MSE, Wishes, sitting with an ice cream and just watching the castle. My daughter and I ride Dumbo with little to no wait after Wishes. Especially if its a midnight closing. Honestly all the rides except Space Mountain and Seven Dwarves thin out after Wishes.
Definitely TTA. Love Jungle Cruise at night, particularly when the Skippers go off script. Alladin during the fireworks is a special treat. Slowing down and really enjoying just being there.
One thing I had forgotten and hadn't seen mentioned. The Electrical Water Pageant. You have to leave the park and go out to the bay near the ferry, but it's really cool. It doesn't take very long.
Wander around Adventureland! I love it there at night. We like to ride the Jungle Cruise and Aladdin at night, and grab a dole whip! I also like going to Frontierland and riding BTMRR and Splash at night. If you wait late enough, these usually don't have much of a wait.
Lots of things others have mentioned. Definitely Hall of Presidents, TTC (People Mover), Carousel of Progress (if open), and a dole whip. We always share a cinnamon bun at Gaston's. Did anyone say Country Bear Jamboree?
It's a good time to eat and try new things you've never experienced before. Ever eaten outside at Casey's? Or one of the other many quick service places at MK? Just bring your food outside and find a table or bench - great people watching!
We love doing the Pirate Adventure in Adventureland at night! The recruiting center is on the path between Pirates and Splash. We've done all five maps on a summer's evening and the effects are really cool at night! Adventureland tends to be pretty empty in the evenings and it's much cooler as well.