In the animal kingdom:
Swift: these can fly up to 106mph on the level.
Greyhound - dog bred for speed. Note legs very thin cross sectional area, stunted tail.
Dolphin - drag coefficient 0.0036 - do you see vortex generators anywhere here?
Eagle
Human Powered:
Varna Diablo II, Cd = 0.02.
Virtual Edge, Cd = 0.011.
The thing unifying all of these is that they are composed of streamlined bodies. Their leading edges all start out quite blunt, curve back smoothly, followed by a much more gentle slope at the rear. Even things that appear to "stick out" are actually just more streamlined bodies only on a smaller scale, such as the fins of the dolphin, the wheel fairings of the hpvs, the rear legs of the greyhound, and the wings of a bird.
We see no vortex generators on any of them, because there aren't any real areas of turbulence that a vortex generator could improve. And the shapes are very, very smooth.
To apply it to our cars, the first areas to obviously clean up are the underbodies of our cars, the wheel areas, and doing something about that rear turbulent area.
Mighty Mira 
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