See the way the leading edge of the vbertical tail meets the fuselage. The A320's is abrupt, the 737's is cranked....
this and the winglets are how I used to distinguish, used to get confused with the noses. Thanks for the replies on this thread, the next flight I take I'll keep a lookout. Out here we only get A320s and B737s, only now you see a few ATRs all over the place.