Kibacorp has an interesting alternative to using an Arduino with a Pi.
Welcome to ISaAC, a small form factor programmable 32-bit Experimenter, featured on the front cover of August 2014 Nuts and Volts. All the information you need to install and operate ISaAC ( ISaAC Python Libraries, ISaAC technical manual) is on this web site
ISaAC is available for purchase from Nuts and Volts store web site.
The ISaAC or, Ideal System and Application Circuit, is used as an add-on board for the Raspberry Pi (Raspi). ISaAC is designed for rapid application development and ease of use. No special programming is required, as the ISaAC comes pre-programmed for the Raspi with an Application Programming Interface (API). The API provides for Raspi power control and external system power +5VDC on/off, an on board EEPROM for read/write of both data, a 100 year Real Time clock calendar (RTCC) with multiple programmable alarm capabilities, 4 analog digital converter (ADC) conversion inputs, a programmable digital analog out (DAC) signal output, 13 digital I/O, and dual pulse width modulation (PWM) outputs for servos and sound.
Find more on Nuts&Volts web site