The standard connector for nonmicro helis is the 3.5mm bullet-style connector. These work well for up to 70 amps and are supplied with Schulze controllers.
For the main motor of FP micro helicopters and for tail rotors of micro helicopters, the most commonly used connector is the crimp pin from a D-sub connector. These are good up to about 4 amps and are available from Jameco Electronics; the female pins are part #43369 and the males are part #43377
For the main motor of CP micro helicopters there really is no standard. I personally use the MP Jet 1.8mm gold connectors, which are available from Aircraft World.