Ride a shetland pony:

Enter KANAHOOKA as a code at the cheats screen.
Unlimited energy:

Enter PHAR LAP as a code at the cheats screen.
Unlock all bonuses:

Enter GENIE IN A BOTTLE as a code at the cheats screen.
Ballistic rider:

Enter TANTALUS BIG AIR as a code at the cheats screen.
Perfect horse stats:

Enter TUDOR PARK REGIME as a code at the cheats screen.
Fireworks in the snow:

Enter CHRISTMAS SNOW as a code at the cheats screen.
Big head mode:

Enter BIGHEAD as a code at the cheats screen.
Development team:

Enter DEVTEAM as a code at the cheats screen.