Here is a description from a dog breed book.
Ears set high, can be cropped or uncropped, uncropped ears should be a half rose or prick
Head is broad, pronounced cheek muscles, has distinct stop.
Back is fairly short, sloping slightly to rear.
Tail short but not docked (to me their tails look kinda like a water pump handle)
Forelegs set wide, straight
Color: any solid or partial color, but more than 80% white, black and tan, or liver are less preferred. (most of the Pit Terriers I've seen have white markings on mainly their legs/feet, chest/neck, and face.)
They also have a springy gait, most are agile and stocky. They have a very short coat and almost almond shaped eyes. Their eyes are fairly small in size and some Pits even have green or gold eyes.
Most Pit Terriers have a few wrinkles on their forehead area esp. when their ears are up 'in attention'.
Hope this helps somewhat. :P