The connector used on TinkerKits and the Arduino Esplora is a 3 pin Molex connector. These may be familiar from some 3 pin PC fans which used them for power, gound, and PWM speed control.
The connectors are also available from many electronics suppliers. Sparkfun sells them for $0.45 each (pins sold separately). Google 3 pin female molex will also show you other sources.