The Arduino Mega 2560 is a microcontroller board based on the ATmega2560. It has 54 digital input/output pins (of which 14 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.
The Mega 2560 is an update to the Arduino Mega, which it replaces.

Techical Specifications:
Microcontroller : ATmega2560
Operating Voltage : 5V
Input Voltage (recommended) : 7-12V
Input Voltage (limits) : 6-20V
Digital I/O Pins : 54 (of which 14 provide PWM output)
Analog Input Pins : 16
DC Current per I/O Pin : 40 mA
DC Current for 3.3V Pin : 50 mA
Flash Memory : 256 KB of which 8 KB used by bootloader
SRAM : 8 KB
EEPROM : 4 KB
Clock Speed : 16 MHz
For more information, please visit this products data sheet.