How Things Fly is an great site I just learned about from Larry Ferlazzo. It is an interactive site from the Smithsonian that explains flight in a variety of ways. Topics include forces of flight, gravity and air propulsion, aerodynamics, structures and materials and flight dynamics.
Students can design and fly their own virtual airplane and there are hands on experiments to do.
This is a great resource for teaching physics and physical science, as well as about flight. Students love airplanes and flight, so this is a good way to get them interested in science.
Microsoft Flight Simulator now Free! Great STEM Resources
Orbiter Space Flight Simulator - free for Windows computers
Century of Flight - History of Aviation