The T-Cobbler is an add-on prototyping board specifically designed for the 2x20 connector-type Raspberry Pi and can break out all those power, GPIO, I2C, and SPI pins from the 40-pin header onto a solderless breadboard. This set will make "cobbling together" prototypes with the Pi super easy.
You will also need the ribbon cable for this breakout board.
All pins are clearly numbered and make prototyping so much easier.