There should be an Oscar for "best ensemble cast"
LA Confidential is good reason for this. As Guy Pearce, Russell Crowe and Kevin Spacey all gave Oscar worthy performances, but with them all being in the same film there was an argument at the time they split the vote whereas if only one of them was that good they might have stood a chance.
I agree that there should be a best ensemble cast Oscar
Too many times someone who gives an outstanding performance in a film alongside other outstanding performances get over looked.