A319-A321 have tiny winglets.
A319 - one emergency exit over the wing.
A320 - two emergency exits over the wing.
A321 - four doors - no emergency exit over the wing.
B737 - dont have the visual differences between them. The -800 and -400 have 2 emergency exits. B737s can be easily spotted by the engine shape.
MD-11 - 3 engines and winglets.
DC-10 - 3 engines without winglets.
B757-200 - 5 doors.
B757-300 - 6 doors.
B777 - the engine that a 7 foot person can stand inside!