[Update: discuss on Hacker News]
This is the Pi Crust:

It lives at http://picru.st/.
It’s a little PCB I designed to make it easier to experiment with electronics and the Raspberry Pi.
You stick it on a Raspberry Pi, like this:

Some features:
- Really compact – sits inside the surface area of the Raspberry Pi and adds less than 2mm to the height. If you have a case for your Raspberry Pi, this board may well fit inside it.
- Pins are grouped together: GPIO, I2C, SPI, UART and power.
- Every pin is clearly labelled.
- Connections: 2 x SPI, 2 x I2C, 1 x UART, 8 x GPIO.
- Uses female headers instead of male headers – you can poke jumpers right in.
- Lots of GND and 5V pins – you need those guys a lot. These pins are duplicated where it makes sense (e.g. within the UART, I2C and SPI groups).
- All thru-hole components – you can solder it yourself.
- Cheapety cheapy cheap.
- Open source hardware.
There are lots of other boards out there, but this is unique in that it fits nice and snugly against the Pi, keeping your projects compact.

Now you can easily find all those pins:

Find out how to make one for only a few $ at http://picru.st/
[Update: discuss on Hacker News]