Different ways to spoke
 

I know there are different ways to thread spokes on a bike, what are the differences, pros, and cons?

From http://sheldonbrown.com/wheelbuild.html#spoke_patterns

Higher cross numbers cause the spokes to leave the hub flange more nearly at a tangent. This makes them better able to withstand the twisting forces of hard pedaling in low gears, and also braking forces in the case of hub brakes.

See also http://www.terminalvelocity.demon.co.uk/WheelBuild/