My recent favorite is ...Bd7-c8. I had a plan to play ...f4 and ...Bf5 with a winning attack, but my opponent could exchange off the bishop for a knight if I played ...f4 immediately. I just stuck it on the back rank out of harm's way and it turned out there was nothing he could do with the extra tempo.
A couple of moves later I got to play a double queen sacrifice (...e1=Q+ Nxe1 Qxe1+ Rxe1 Rxe1#) but it was brutally obvious, whereas ...Bc8 had some finesse.
a3