Development Gag: In the Video Games ending, jumping down the elevator shaft after completing the Portal map will bring the player back to the office, as it appeared in the original mod.
Doing It for the Art: Kevan Brighting's voice work as The Narrator is not only found in both the original mod and the HD Remix release, but he has provided his soothing tones for a little-watched seven-minute YouTube video called The Aperture Parable, in which he describes how the nature of The Stanley Parable is similar to that of Portal, and also done voicework for a number of other Stanley Parable fanworks. He also role-plays as The Narrator on his Twitteraccount, continuing the never-ending adventures of Stanley.
Urban Legend of Zelda: There are a lot of rumors that it is possible to defuse the bomb in the Countdown ending. Since there are so many useless buttons and other things to interact with in the Countdown Room, this was inevitable.
The Museum ending, aside from showing off a lot of the game's assets, demonstrates several unused and unimplemented ideas, including further Ask The Narrator trailers (in the vein of the Raphael trailer) and a battleground ending.
A planned ending, where the game turns into a sci-fi First-Person Shooter game with its own narrator who ends up in conflict with the Narrator, was never implemented, but shows up in the Museum.
An iOS version of the game (with altered scenarios to fit a mobile environment) was intended to be developed around the same time the HD Remix was, but due to communication issues between the development team and Cakebread, it was scrapped. Unused Narrator lines can be heard here.