The Hitcase at CES 2013 makes a case for being a leader in the rugged iPhone case market. Its size and weight means it's not meant to be left on all the time, but it should survive your action sports adventures.
The interior of the Hitcase holds your iPhone snugly in place. Note the rubbery-looking pattern on the right-hand side. This provides shock protection should you take a tumble off your mountain bike at high speeds.