I have seen everything from private jets to 747s and A300s with small upright tails on their wing tips. What purpose do they serve?
They're called winglets, and their purpose is to reduce turbulence at the tips of an airplane's wings. The air pressure on the bottom of a wing is greater than the pressure on top, so when air flowing across the two surfaces meets at the wing tip, it forms a vortex-a miniature tornado. The vortices created by a large airplane are strong enough to flip a smaller plane that is following too closely.