Shields and Modules
Shields and Modules for Arduino, Raspberry Pi and other Microcontrollers
You will find an extensive range of shields and modules here suitable for both Arduino and Raspberry Pi.
It's important to remember that Arduino generally runs in a 5V world and Raspberry Pi in a 3.3V world. So sometimes you may need a voltage converter or a level converter to use a 5V device with a 3.3V microcontroller (or vice versa)
If you are interested in developing your own solutions you will find many suitable products here