The Physics
Frisbees utilize several different effects of physics in their flight. The two main ones that we will talk about here are the "Gyroscopic Inertia" and how the shape of a frisbee causes pressure differences to cause lift more commonly known as the "Bernoulli's Principle" (much like a plane's wing). First the gyroscopic effect.
A gyroscope is a device used to maintain an objects orientation and angular velocity. What is causing this gyroscopic effect on the frisbee is the spin that results from its circular shape and the techniques we use to send it on its way. These techniques come in an incredible divers package, but one thing everyone that I can think of has in common is that they are preformed from the edge of the disc. Not the center of mass, in-fact as far from it as you can be and still be influencing the frisbee. Because we are acting upon the frisbees outer edge here, we are dealing with a distance from the center of mass known as a radius. Combine that with the velocity at the point you are holding the frisbee, then throw some time duration in the mix and you get angular velocity.
This angular velocity is the speed of the rotation of the frisbee and according to Newton's first law: "A body in motion tends to say in motion, while a body at rest tends to stay at rest.", the disc will keep rotating at that same speed until it comes in-contact with something (like a tree, hand, head, etc). And this angular velocity is part of our Gyroscopic Inertia. As Eugene Motoyama put it in 2002, "'Gyroscopic Inertia' refers to the resistance one encounters when trying to change the axis of rotation of a rotating body. We will show that this simply equals the magnitude of the angular momentum." ("The Physics of Flying Discs" p.2). The equation for the angular momentum is:
What Eugene is saying is that the larger L is, the harder it is to change the direction of the whole body. So if you were to throw a frisbee into the wind with a power full throw, it would fly strait longer than id you weakly threw it into the same wind. Another great example of a gyroscope is a top. If you have ever played with a top you know that you quickly get addicted to trying to keep it spinning for as long as possible. You may also have had siblings that, when they saw you having fun, would come over and try to knock the top over, but if they did not apply a large enough counter force the top would just wobble a bit, then keep spinning. As David Featonby put it in 2010, "A gyroscope on a moving platform can demonstrate the way in which a spinning object conserves its spin..." ("Dare we teach tops?" p.6). And that is how a frisbee flies consistently in the direction you intend it to.
Click here to read about Bernoulli's Principle (or on the top of the page where it says "A Frisbee's Flight and Bernoulli's Principle") and how it applies to Frisbees.