This tutorial shows you how to connect Raspberry Pi and Arduino using I2C communication, how to configure it. Combining them does not require your USB port.
Raspberry Pi to Arduino shields connection bridge
Introducing the PiDrive, a high capacity Solid State Drive (SSD) expansion card for the Raspberry Pi B+, A+, and B+ v2!
Check out http://arduinohq.com DiddyBorg - The most powerful Raspberry Pi robot available | PiBorg (Scheduled via TrafficWonker.com)
Cpcdos, Raspberry Pi, Arduino Plus
RaspberryPi Arduino Webcam laser range finder
Raspberry Pi add-on will help you build Lego Mindstorm robots | Ars Technica
RC522 13.56Mhz RFID RF ID Card Reader Arduino Raspberry Pi SPI Interface Adeept
Raspberry Pi + Arduino + Tornado
Go Cortex using Wit-ai on a Raspberry pi connected to an arduino and written in go....
Pi Tank 3D Printed Open Source Smartphone Controlled Raspberry Pi Robot