After completing a flight with a load of skydivers, the pilot “dipped” the left tank and it indicated 15 gallons of fuel. He then flew another flight to 3,500 feet MSL and started his descent. The pilot reduced power to 1,600 rpm and 16 inches of manifold pressure, and applied full carburetor heat. As the aircraft was approaching pattern altitude, approximately 1,000 AGL, the engine quit without warning.