The medium range segment for both Boeing and Airbus is the 737 and the A32X.
Aside from looking at the nose, where the 737 radome is much more pointy than the Airbus.
The Airbus has much more ground clearance, longer and more distinct landing gear. The 737 has small "eye brow" windows in the cockpit, while the airbus does not.
The profile of the tail is also a good way to tell them apart. Where Airbus has a straight angle on the vertical stabilizer. The 737's is a two-angle type, and it's very noticeable.
As a hardcore aircraft-enthusiast, I can give you 500 ways to tell them apart, but some features are hard to see and requires a photo comparison

I tell you what, to to
www.airliners.net and browse the different aircrafts available there, you'll soon begin to notice their differences
