One of the great things about the Arduino platform is the ease with which you can capture and record data for later analysis. One popular example of this has been documented by Mathias Van Moortel who demonstrates how to record time and temperature data from an I2C-interface real-time clock and DHT22 temperature/humidity sensor respectively to an SD card. Doing so is incredibly simple with the example sketch provided, and can become the framework of a more complex system later on.
When putting together your next Internet-enabled Arduino project, or would like a compact Arduino with memory card socket - save time, space and money with the Freetronics EtherTen. Apart from being fully Arduino Uno-compatible, it has onboard Ethernet, microSD socket, full USB interface (so you don't need a costly FTDI cable just to upload a sketch!) and supports optional Power-over-Ethernet.