Dexter Industries, creators of the excellent BrickPi and GrovePi have started a Kickstarter to raise funds for the “Arduberry”.

Here is some blurb from the KS campaign page:

The Arduberry is a simple and inexpensive way to bring Arduino shields to the Raspberry Pi. The device is a shield that slides over the Raspberry Pi and allows you to stack and use Arduino shields. The Arduberry requires no physical configuration to work with most shields. You can write Arduino sketches (programs) right on your Raspberry Pi. The Arduberry will bring the Raspberry Pi and Arduino together, uniting the two greatest hacking systems ever.

Sounds like an interesting one, although not unique, and should be a high-quality product going by their previous projects.

Read more on the Kickstarter page