What To Do: Let's hope you're not going down a hill and that you are driving a manual. If you're driving a stick, use downshifting to slow the car. If you're stuck with an auto, you have to try not to panic and start looking for more crafty plans to stop the car. And remember, a paint job is not as important as yourself or your engine.
See any fields, grassy medians, or hills (not too steep of hills)? Head for those. The dirt, grass and incline can help naturally slow down the car. If those aren't in sight, try to find something less concrete that will minimize damage to done you and your car. Chain link fences are good. Trees are bad.