Open source Wireless sensor platform - Waspmote
"The idea behind the Raspberry Pi to Arduino shields connection bridge is to allow to use any of the shields, boards and modules designed for Arduino in Raspberry Pi. It includes also the possibility of connecting digital and analog sensors, using the same pinout of Arduino but with the power and capabilities of Raspberry."
Raspberry Pi to Arduino shields connection bridge
Cooking Hacks - Tasty Electronics for the Arduino and Raspberry Pi Community.
The have a wide range of electronic products and kits including Arduino, ZigBee, GPRS, Sensors, Servos, Leds, LCDs etc.