If you have Mass Effect 3 for the Xbxo 360, you can start downloading the game/s 1.85 GB "extended cut" ending right now. Boot up the game, click the downloadable content option from the main menu, and you'll find the screen shown above.
I'm checking the PS3 next, though I don't have a copy of the game and I'm currently in download-new-firmware purgatory. I'll update this again when the DLC pops up on PS3. No PS3 version yet this morning.. The PC version is expected in the early afternoon.