Big head mode:
At the main menu, type "big heads".

Extra stunt points:
When jumping, repeatedly press [Print Screen] for extra points.

Extra boost:
When riding up a hill, press [Tab].

Super speed:
Note: This trick requires a Microsoft Sidewinder 3D Pro controller. Set the throttle to control the acceleration. Then while playing any event or mode, move the throttle to around 3/4 Full and watch your speed. It will rapidly increase and go over 100. Be careful, as your turning speed is decreased the faster you race.