How about an Arduino Pro version of the ATmega1280 but with all the pins broken out (provides 70 digital I/O instead of the Arduino Mega’s 54) and operating at either 3.3V or 5V. Make something similar to the seeeduino (http://www.nkcelectronics.com/seeeduino … mbled.html) but without the headers, USB, switches, etc. Although I would suggest running the 3.3V at 10 MHz.
Thanks.