Find the best move! (intermediate)

INSTRUCTIONS: The advantage of the best move isn't as clear cut as it is in regular puzzles, according to rybka its only +0.55 over other moves.  Furthermore, in this puzzle black doesn't have to give you a material edge, in fact he can end the puzzle up material =O!  With those 2 points in mind, find the best move.

Backstory: During maitenance I was bored and playing littlechesspartner, both of us having 30 seconds to think for each move.  He was making horrid moves in the steintz french defense (Nc6?), and he slipped up.  I found and analyzed this move in game in merely 30 seconds.  While of course I already was looking at the board, I am proud about finding this move that comes out of NOWHERE.  Little chess partner fell in 31 moves, a new record =).