Features:

SD card interface works with FAT16 or FAT32 formatted cards.
3.3V level shifter circuitry prevents damage to your SD card.
Real time clock (RTC) keeps the time going even when the Arduino is unplugged.
Included libraries and example code for both SD and RTC, means you can get going quickly.
Prototyping area for soldering connectors, circuitry or sensors.
Onboard 3.3V regulator is both a reliable reference voltage and also reliably runs SD cards that require a lot of power to run.
Works with Arduino UNO, Duemilanove, Diecimila, Leonardo or ADK/Mega R3 or higher.
ADK/Mega R2 or lower are not supported.