This is a right-angle, 24-pin Molex Mini-Fit Jr.™ connector, commonly used as the power supply connector on [ATX](http://en.wikipedia.org/wiki/ATX#Power_supply) motherboards. Two rows of twelve pins are broken out two rows of through-hole male headers. See the datasheet below for pin spacing dimensions.
Pair this connector with a standard computer power supply and you can source a number of different voltages (+3.3V, +5V, +12V, -12V, -5V) to your project.[
* [Dimensional Drawing](http://www.sparkfun.com/datasheets/Prototyping/Connectors/ATX-RA.pdf)