We have developed a board which has an ARM Cortex-M3 micro in the Arduino format. This is definitely not an official board, and by using a
72MHz 32-bit processor with 512KByte of Flash we guaranteed there would be a few changes from the 10MHz Atmel ATmega168 in the Arduino... But we tried to keep as close as possible to the Arduino spirit.At least the connectors are in the same places and the functions on the pins are the same, though there are many more options. More details and pretty pictures at
And I would be happy to answer any technical questions.
Tim