http://www.kwaninternational.com/ima...car%20race.jpg
This has two ideas that are good. the hood hump goes out to the edge of the windshield, and the air intake is almost embedded in the hood of the vehicle (think LARGE NACA duct). The red and black car also has canards in front of the exhaust (barely visible).
I am not sure what the rules are for the underbody/undertail. I would say that the number one thing that you can do is to create as much down force using the shape of the vehicle so that you don't have to have a wing create that force (which is also providing aero braking). Making air take the long way underneath and the short route above (low and high pressure, respectively) Sounds like a fun project.