The Boeing 717 was inherited from the merger with McDonnell-Douglas. It is clearly a DC-9/MD-80 derivative. It has an MD-87 like tail, and large diameter engine nacelles with singles exhausts.
To recognise this trijet airliner with three engines at the rear fuselage and a T-tail you can look for the typical Boeing nose with two eyebrow windows, and the two wheels on each main landing gear leg. The other aircraft in this category have four or six wheels on the main landing gear.
To distinguish the second, third and fourth generation Boeing 737 from similar twin jets look at the cockpit windows: these are the same as or similar to that of the Boeing 707 and 727. The older versions still have the two "eyebrow" windows above the normal cockpit windows. These 737s have a large triangular dorsal fin.
The first generation Boeing 737 has long nacelles under the wings, extending before the leading edge and beyond the trailing edge. For the rest it has the typical Boeing 707/727/737 nose with eyebrow windows, and a tall tail with hardly a dorsal fin.
If there is one iconic jet airliner, it is the Boeing 747 with its partial upper deck. The "hump" comes in different lengths, but not along the the whole fuselage, and this is what makes it different from the Airbus A380.
The Boeing 757 has a lot in common with the Boeing 767, but has a narrower fuselage resulting a different nose. The most likely you are going to mistake the 757 for a Tupolev 204 however. Look at the cockpit windows and winglets to keep them apart.
Typical for the 767 are the four wheel main landing gear bogeys that are tilted forward when the aircraft is of the ground. Additionally, the tailcone of the 767 is pointed. The lower sides of the cockpit side windows form a V shape.
Essentially the Boeing 777 is a “blown-up” 767, but there are specific recognition points The tailcone of the 777 is squared off and the main landing gear has six wheels per leg. The bogeys are not tilted.
The Dreamliner looks similar to the 767, 777 and A350, but it is still easily recognisable. The 787 has only four cockpit windows. The wings with raked wingtips are curved up and the backend of the vertical tail is slightly pointing up like a shark fin.
This large biplane has one radial piston engine in the nose and two in between the wings. The lower wings have a smaller span than the upper wings. Most versions have a single vertical stabiliser, but some have additional fins on each side, about halfway the horizontal stabilisers.