micwhite wrote:
Perhaps there's something better, but a quick look at Nxd4 seems promising:
Nxd4 Qxd4 Rxe3 Qxe3 d4 and black is picking up two pieces for the rook and white still hasn't castled.
Edit: Actually, there seems to be a problem with that. After d4 white has 0-0-0! The search goes on! ☺
Would you rather I just said 'yes' so others can guess too?
guessing moves is totally fine (even if you get it right) but if you end up looking what the answer is with an engine, then do not spoil it 
Black to play and win by -3.6!
White is preparing to castle queenside.
Can you find a move that wins material?