Well, I guess it wasn't as hard as I thought, or the players on this board are just very good.
The answer is Bd7; anything else allows black to end the attack.
I though it was so counterintuitive because white's queen is hanging and the best move is to hang another piece on a square that it could be taken for free by any of 3 pieces.
Waitzkin describes it as "throwing a rock in black's machinery." I love that description.
Also, you're right that black is not "doomed" after that. After Nxh8, Nxe6+ leads to forced mate. After Bxd7, Qxg7 leads to mate or big material loss for black. Rxd7 leads to Nxe6+ and loss of queen or mate for black.
After Qxd7, black survives, but after a long variation, white still has a nice attack. I forget the variation off hand- I'll have to fire up CM-GM when I get home (I'm at work now). Any other move by white and the attack is over and they go to the end game.
Without having seen the game, anyone want to guess who was playing white? (This is not from the game, it's just a variation that could have arisen during the game.)