Air
No commercial use has yet been found for photovoltaics in flight, although there is considerable military interest in solar powered unmanned aerial vehicles (UAVs). Many demonstration solar planes have been built, some of the best known by AeroVironment.
Manned solar planes

Gossamer Penguin,

Solar Challenger - This plane flew 163 miles from Paris France to England on solar power.
UAVs

Pathfinder and Pathfinder-Plus - This unmanned plane demonstrated that an airplane could stay aloft for an extended period of time fueled purely by solar power.

Helios - Derived from the Pathfinder-Plus, this solar cell & fuel cell powered UAV set a world record for flight at 96,863 feet (29,524 meters).
Future projects...