I2C Duino

uCHobby has a helpful primer on interfacing electronic components via the handy I2C protocol and Arduino –

I²C uses only two bidirectional open-drain lines, Serial Data (SDA) and Serial Clock (SCL), pulled up with resistors. Typical voltages used are +5 V or +3.3 V although systems with other, higher or lower, voltages are permitted.
What exactly does the I2C protocol and usage mean to the average robot builder? Well, it can mean a lot of different things,such as easily accessible devices like temperature sensors, accelerometers, and even setting up a small on board network on a robot.

Introduction to I2C

Bare Bones Arduino Board Kit (Unassembled)