Getting the achievement "Click On Door 430 Five Times". It's an exact opposite of That One Achievement, in that it's actually really fun to get. When you click on door 430 five times, the narrator asks if the player is just doing this for the achievement. The narrator then says that's not worth the achievement, and has the player running around the office interacting with seemingly random stuff, getting more and more excited as it progresses. The procedure culminates with a Big "YES!" from the narrator once the achievement unlocks. What's more awesome is the achievement's badge.
There are people who fairly beat the Baby minigame. And yes, it really is 4 hours. The Art ending may not be as spectacular as they wanted, but they sure as hell earned it!
The "Real Person" ending while it is a bit of a Guide Dang It!, by unplugging the phone which normally leads to the Pawn ending. It completely makes the story go Off the Rails to the point where even resets can't fix the game, and eventually the Narrator decides to prevent you from taking control of Stanley anymore, leaving him to beg a motionless Stanley to make the iconic "two door choice" to no avail, which gives off the impression for as much as the narrator boasts that he is in control, he needs the player in order to make choices to advance the story at all. Roll credits, and realize that you've kind of beaten the Narrator at his own game.
There are still some people who keep trying to find a way to stop the Countdown Ending. Even though the Narrator clearly asserts that there isn't.
In the basement, according to the narration - Stanley suddenly realized, and proceeded to shout out, "I'M DREAMING!" before becoming lucid and flying through a black field of stars. Bad end, but still - not many stories have captured the excitement of a lucid dream so well.
You might consider the Zending to be one if you really don't like the Narrator. Especially if you move back and forth from the Zen room and the Stairs room, toying with his emotions in the process.
For most games, once you own the main game, there's no reason to ever play the demo as it's just a small chunk of the whole. Not the case here. The demo for The Stanley Parable shares almost no content with the main game. Despite this, it does a far better job at illustrating what to expect from the main game than most demos could ever hope to do.