Originally posted by geo1004:
757 narrowbody, 767 widebody
... or check the pay stub of the pilots! 
[(edited 06-08-2000).]
The 757 & 767 has the same rating, therfore if you get certified in one and can fly the other. They were developed at the same time and have identical cockpits.
The 757 and 767 have different amount of doors. The 757 has 6, while the 767 has only 4, yet they both have 4 window exits over the wings.
The A319 & A320 can be told apart based on the window exits over the wings, the shorter A319 has two, while the 320 four.