Ninja Turtles 1
Faxanadu
Adventure Island
Ghouls and Goblins
Wizards and Warriors
Bubble Bobble (the boss at the end is impossible)
Megaman 2,3,4
Festers Quest
Kung Fu
Paperboy...
there are a few others (Master blaster) that I can't think of right now, but these I found to be quite difficult and have gotten to the end of the game without beating it