Extreme sports

Here is a list of extreme sports:

Earth:
Skateboarding, Longboarding, Mountain Boarding, Sandboarding, BMX, Motocross, FMX, Aggressive Inline Skating, Mountain Biking, Caving, Slacklining, Absailing, Rock Climbing, Free Climbing, Bouldering, Mountaineering, Parkour, Sand kiting, Zorbing

Water:
Surfing, Long/short, Body boarding, Waterskiing, Wakeboarding, Kitesurfing, Windsurfing, Cave diving, Flowboarding, Paddle surfing / Stand up paddle, Kayaking, Cliff Jumping, Coasteering, Scuba Diving, Knee Boarding, White Water Rafting, Skim Boarding, Jet Skiing

Snow and Ice:
Snowboarding, snow skiing, Ice Climbing, Snowmobiling, Snow Kiting

Air:
Base Jumping, SkyDiving, Wing Suiting, Bungee Jumping, High-lining, Hang Gliding, Paragliding.

You can download a useful PDF document on sports here.