Teensy 3.1 ARM cortex M4 dev board

The Teensy line of development boards seem like some pretty powerful and compact (read teensy) microcontroller boards.  The latest version, Teensy 3.1 uses a Freescale 32bit ARM Cortex M4.  With 262K of flash, a whopping 64K of RAM, and running at 72Mhz, the Teensy 3.1 seems to be on the higher end of the horsepower range.  At under $20, I wouldn't mind giving it a try.

Loading code into the Teensy is accomplished via a boot loader, much like Arduino.  So, no JTAG/Debugger required.  Also, the website mentions that the Teensy boards are "mostly" compatible with Arduino sketches with the Teensyduino plugin to the Arduino IDE.

There are several USB examples for implementing various USB interfaces.  Keyboard, mouse, serial and HID are available.

The teensy 3.1 is $19.80 and is available here, check out the other Teensy boards.
http://www.pjrc.com/teensy/index.html

Crazyflie, the ARM quadrocopter dev kit!

 I like seeedstudio, they are creative, open source and geared towards tinkerers.  The Crazyflie is a great example if why this shop stands out.  It's a tiny (90mm square) quadrocopter.  And it's open source, in fact seeedstudio is counting on the community at large to develop it.  It's controlled via a 2.4ghz link and a PC.  And it can be wirelessly updated if you don't have a jtag debugger.  Based on a STM32 ARM cortex M3 running at 72 MHz, its got a lot of processing horsepower.  Check out the video!

Build your own swarm, I wonder if you could get a camera small enough for FPV.  This little guy can fly around 7 minutes on a charge, and can lift around 5-10 grams.

Starting around $116

http://www.seeedstudio.com/depot/crazyflie-nano-quadcopter-kit-6dof-bccfk03a-p-1526.html?cPath=84_114