Ril3y demonstrates an I2C magnetic compass sensor (Sure Electronics DC-SS503) with the Bus Pirate.
Don’t forget that Ril3y has stylish laser-cut acrylic cases for the Bus Pirate (seen here).
Get a Bus Pirate v3b for $30, including worldwide shipping at Seeed Studio. Adafruit also has the Bus Pirate and probe cables in stock and ready to ship.