My list of extreme sports:
Shape of board depends on riding style, and rider himself. Wiki says that bodyboarding is fastest growing extreme water sports all over the world.
Canoeing: extreme canoeing (a.k.a whitewater canoeing or whitewater racing). These extreme guys race specialised canoes and kayaks down a dangerous whitewater rivers. There is also such a class like Extreme Canoe racing, that includes much more complicated rapids, leave it for real pros 🙂
Free Running: Parkour
Le Parkour: Free running
BMX: Vert, Street, Dirt, Freestyle (Flatland)
White Water Rafting: