From the elinux wiki: There are approximately 16 spare GPIOs, which are brought out to 1.27mm pin-strip. Voltage levels are 3v3. The connector choice is delibe

From the elinux wiki: There are approximately 16 spare GPIOs, which are brought out to 1.27mm pin-strip. Voltage levels are 3v3. The connector choice is deliberately annoying to connect to directly; there is no over-voltage protection on the board so the intention is that people interested in serious interfacing will use an external board with buffers, level conversion and analog I/O rather than soldering directly onto the main board. We also bring 2x I2C (3v3), I2S and an SPI (3v3) interface out to the same connector. We support one slave interface for I2C and one for SPI. http://elinux.org/RaspberryPiBoard http://elinux.org/RaspberryPiBoard