Arduino Mega 2560 R3 (Atmega2560 - assembled) - Mega!
The Arduino Mega 2560 is a microcontroller board based on the ATmega2560 (datasheet). It has 54 digital input/output pins (of which 15 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Mega is compatible with most shields designed for the Arduino Duemilanove or Diecimila.
Specs (from http://arduino.cc/en/Main/ArduinoBoardMega):
Input Voltage (recommended)7-12V
Input Voltage (limits)6-20V
Digital I/O Pins54 (of which 14 provide PWM output)
Analog Input Pins16
DC Current per I/O Pin40 mA
DC Current for 3.3V Pin50 mA
Flash Memory256 KB of which 8 KB used by bootloader
Clock Speed16 MHz