The Buffalo can be regarded as a Caribou with turboprop engines and a T-tail. For the rest they are similar in appearance: the fuselage with a sloped up rear, nose and cockpit, and gear retracting in the nacelles.
The Twin Otter has the fuselage and wings of the DHC-3 Otter, mated with two turboprop engines in the wing's leading edge, a fixed nose wheel landing gear and a nearly rectangular cruciform tail.
The Dash Seven commuter aircraft has a T-tail, four turboprop engines under the wings and a main landing gear retracting forward in the inner nacelles. Together, they give it a unique appearance.
The Dash 8 series has four main versions, of which the longest is shown on the photo above. A clear recognition point are the cockpit windows, which look much like those on the Canadair Challenger, Canadair Regional Jets and Bombardier Global series.
deHavilland DH104 Dove
The cockpit popping out of the front fuselage is one of the main characteristics of the twin prop aircraft. Other features are the rectangular cabin windows with rounded corners, and main gear retracting outward in the wings. Normally the vertical stabiliser is curved from the dorsal fin to the tail cone, but there are conversions with a different tail.
deHavilland DH106 Comet
The world's first jet airliner can be recognised by the four jet engines in the wing roots, the nearly straight vertical stabiliser and the main landing gear retracting outward in the wings. It has a circular cross section fuselage.
deHavilland DH82 Tiger Moth
Britain's primary trainer of the 1930s and 1940 has a very characteristic vertical stabiliser compared to similar aircraft. Other features include the inline piston engine and two parallel struts between the outer wings.
deHavilland DH83 Fox Moth
The Fox Moth is basically a Tiger Moth with an enclosed cabin. This is directly behind the inline piston engine and features two big windows on each side. The pilot sits behind and above the cabin. The vertical fin has the typical deHavilland shape.
deHavilland DH89 Dragon Rapide
The DH89 has a similar external appearance as the DH84 and DH90, and to a lesser extent the four-engined DH86. The Dragon Rapide's characteristics are tapered wings with elliptical wing tips, fairings around the main gear and five cabin windows.
deHavilland DH98 Mosquito
The two enormous Merlin liquid cooled piston engines already make up half of the length of this iconic bomber/fighter. Their props are turning near the tip of the nose. Furthermore, the Mosquito has a small vertical stabiliser with the shape of half an oval. The single wheel main gear retracts rearward in the nacelles.