Operation Darkness with no one dying. Not really hard, just very cheap.
The only thing I can think of right now is Castlevania Rondo of Blood hard mode. I'm not really sure what the consensus is for difficulty on most games.
EDIT - Thought of some more that gave me trouble: Rengoku, Strange Journey (but that's mostly because of the final boss), and Gitaroo Man (not sure if this is because you can't calibrate it though)