Are there any expansion boards available for the Raspberry Pi for use with the GPIO?
Adafruit has unidirectional and bidirectional Logic Level Converters among other goodies for the RasPi.
BitWizard B.V. also carries a range of I2C expansion boards and accessories,
RaspberryPI has also discussed the Gertboard, but I have yet to see pricing and availability details.
The Pi-Face looks like a great expansion board.
From the website:
- Allows you to control lights, motors etc and monitor digital inputs, switches, etc.
- Four switches and four LEDs on board for rapid prototyping
- Two onboard relays (10A) for easy control
- Buffered to protect the Raspberry Pi; high-current open collector outputs and schmit trigger buffer inputs
- Credit card size, stacks on top of Raspberry Pi
- Easy to connect with screw terminals
- Easy to program with C and Python libraries
From the looks of things this will allow you to take input from a myriad of sensors, and easily allow you to interface your Pi with external components like switches, relays, lights etc
Seeed Studio has Grove Base Hat for Raspberry Pi which provides GPIO connectors.