The Raspberry Pi is a neat piece of hardware, but it’s not so easy to breadboard with. To solve the problem, LadyAda created the Pi Cobbler breakout board, which makes it easy to breadboard your R-Pi circuits.
Fritzing is an open-source software package that (among other things) gives you a virtual breadboard where you can mockup designs before making them physical. To make it easier for you to use the R-Pi on your virtual breadboard, we created a Pi Cobbler for Fritzing (shown above, connected to a rotary encoder and LED).
You can get our Fritzing Library over at GitHub.