Halo: Reach Easter Egg - Master Chief

In the last cutscene of the Pillar of Autumn level, the one after Rally Point Bravo, as the scene cuts to the interior view of the cruiser's hangar bay while Captain Keyes is landing the Pelican, hold the right control stick right. By doing so, you can see Master Chief John-117, laying in his cryo-chamber.

This reaches out to Halo: Combat Evolved, where the Chief is released from the chamber in the beginning of the game.