I voted for an unimaginative spade. I figure it isn't a Diamond for that's what most of the people answered so, could it be a club? I don't understand why partner didn't bid another suit on his way to sac (maybe because then he would have needed to sac at the 5 level?) to ask for a lead, but as he couldn't fit bid clubs, I'm guessing you wanted us to think about a club lead.