ARM Cortex-M3 development board
On Chaos Communication Camp 2011, I bought an Olimex LPC-P1343 development board for the H.A.C.K. in exchange for one and a half Mateist T-Shirts. Thus it is available for everyone to tinker with, especially, if an Arduino (or any PIC) is just not enought for the task. It is currently located in the middle of the project shelves, on the shelf labelled dnet, in a red-black-blue OLIMEX box. The USB connector is micro USB, so grab a cable from home if you want to ensure that you can use the board.
The Cortex-M3 is a 32-bit CPU core fully supported by GNU binutils, GCC and GDB. NXP LPC1343 is a small microcontroller running the core at up to 72MHz, with 32kb flash, 8kb RAM, a built-in generic USB device peripheral and many other features.
It was used on a workshop at 27c3, the code used there can be found in the attachments along with the schematic and user manual of the board, and two PDFs about the CPU itself.
The r0ket given to every attendee of the camp is also built on the NXP LPC1343F. Build instructions.