All of these:
BASE Jumping
Bodyboarding
Extreme Canoeing
Cliff Jumping
Freestyle motocross
Hangliding
Ice Climbing
Jet Skis
Kite surfing
Le Parkour: Free running
Extreme Biking
BMX: Vert, Street, Dirt, Freestyle (Flatland)
Trials
Mountain Biking: Downhill, Freeride, Northshore, Slope Style and other
Paragliding
Rock Climbing
Sand Boarding
Sand Kiting
Extreme scootering
Skateboarding
Extreme Skiing
Snowboarding
Snow-kiting:
Surfing:
Windsurfing
White water rafting
Wingsuit sky diving

it depends on what scares you the most. I'm afraid of heights so I guess skydiving would be the most extreme sport for me

Maybe base jumping? I think it must be wild jumping of fix objects and not having less time to open the suit or something.. it's fast and so not secure!

I think cliff jumping is the most extreme. the impact may be strong and you never know what you can hit in the water.. it seems pretty dangerous!