Minecraft Easter Eggs
If you bake a cake for the first time in Minecraft, you will receive an achievement titled 'The Lie', a reference to Valve's 'Portal' series in which a recurring theme is a cake to be rewarded to you at the end of the game, and the writing on the walls in some secret alcoves saying 'The cake is a lie.' many times.
HIM Easter Egg
If you are on a foggy day, look closely. If you are lucky, you may see a person with default skin but with white eyes, dubbed by Notch, 'Herobrine,' or simply HIM. You may even (most rare thing you can think of) find him in the Pocket Edition of Minecraft (the only mob).
Samus' Helmet from Metroid
If you put a pumpkin in the helmet section of your armor your HUD will turn into the HUD of the galactic bounty hunter Samus Aran from Metroid. (No you won't get any missiles)