The "expanded" ending of Mass Effect 3 is live for you to download right now, people. Four completely new cut-scenes depending on which of ME 3's ending you earned through the game. One of the new endings, "Refusal," is actually an entirely new choice that can be made.
The honest thing to do is install the update, go back to your save game and check it out... but if you want to save yourself the trouble, I've embedded all four of the new endings under the "Read More" tag. This post is literally ALL SPOILERS. So don't look if you don't want to be spoiled.
Mass Effect 3: Control Ending
Mass Effect 3: Synthesis Ending
Mass Effect 3: Destroy Ending
Mass Effect 3: Refusal Ending