#1 Tali and Garrus Caught in the Act
If you always thought it was strange that Commander Shepard was the only one getting nasty on the Normandy, you'll appreciate this final easter egg. Provided you're not romantically involved with either Tali or Garrus, late in the game they'll hook up, and you'll actually be able to walk in on the two of them doing some — ahem — calibrations in the main battery.
The conversation that follows is amusing, but don't watch this video if you're early in the game, as it's easily the most spoilerific on this list.
