From Wikipedia:
The Lotus effect refers to the very high water repellency (superhydrophobicity) exhibited by the leaves of the lotus flower (Nelumbo).[1] Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface which enables minimization of adhesion.
This effect can easily be demonstrated in many other plants as for example tropaeolum, cane, or columbine, and on the wings of certain insects.
And a cool demonstration of the effect.
(via Unreasonable Faith)