The Pi-cobbler from Adafruit consists of a 26 pin ribbon cable, a custom PCB, a ribbon cable socket and a set of header pins. It comes in kit form and you are required to solder the cable socket and the header pins to the PCB. This is a relatively simple task.
You can cause damage to your Raspberry Pi if you incorrectly connect the GPIO pins. The Pi cobbler makes the task of prototyping circuits easier and a little safer by allowing you to connect it to a solderless breadboard.
The PCB has all the pins labelled nicely so there is no need to keep any pin-out documentation at hand.
The gallery has more pictures of the Pi Cobbler in action.Gallery