If it was my choice, after Shepard pressed one of the "buttons" he goes on a mystical journey, leaving his body behind, he watches the ending from afar, afraid and angry, he somehow goes back in time and shows up as the past Shepard is about to press one of the buttons, he has a special weapon (EDIT: How about to get this weapon you must go through memories of your whole Mass Effect journey, you know like what you sacrificed to get here, what have you gained and etc), he fires it, it kills the VI child, shattering the past Shepard's fear and everything else, a holographic console opens up from the VI's body after it was killed, the two Shepards combine into one true Shepard.
Also Marauder Shields recovers and becomes your best friend after he comes up and shoots the VI body since it was Harbinger all along and he was about to kill shepard and Marauder Shields says he quits being a soldier of harbinger then finishes him off.
The true Shepard quickly runs to the console, hooking EDI up to it, she edits the program quickly to just make the explosion effect only the reapers and the reapers only, as soon as Shepard is about to press the enter command button on the console Harbinger appears and almost kills Shepard again, but Shepard has one last battle (Dunno how, epic fist fight?), Harbinger goes down, the button is pressed, all reapers die, the catalyst is exploding, the normandy shows up, Shepard runs to it and jumps, (if paragon you survive, if renegade you die, EDIT: Okay that would be unfair, how about you die if you didn't get enough readiness?), good shepard gets on board and they escape.
Epilogue. (mine at least)
A tv shows a picture of Shepard accepting multiple prizes, awards and promotions due to his actions. It zooms out, Ashley enters the room/house with a box, she sees the tv and calls for Shepard, he comes in and sees the tv, he makes a wise ass comment, he puts down the box and grabs Ashley tightly and they kiss.
More clips show up for each of the races/other heroes as they narrate what has happened to them and their race.
Eg. Tali narrating how the geth and her race are getting along and rebuilding the planet.
Liara telling how she returned to her own planet and began rebuilding too and became the next asari councilor
Wrex saying how he has became leader of the Krogan and that they have found a new planet and have began to create children.
And etc for others.
Then a brief clip of Shepard and Ashley with every other surviving crew member gazing out into the ocean as Shepard narrates their outcome and how he has overcame hardship and etc.
The true END!
EDIT: Also break and add bits and pieces to make your happy well deserved ending. (Someone get this to Bioware damn it!)