Which way a spin vector points is a matter of convention. See
http://en.wikipedia.org/wiki/Right-hand_rule. As far as the maths is concerned, it doesn't matter which way you choose as long as you are consistent. For the flight of a Frisbee or a gyroscope, there are are two spin vectors of interest: its angular momentum and an applied torque. Using the same convention for each of those (and using the convention for direction of cross-product that matches the order in the equation) produces a resultant precession in the same spin convention.