I'm connecting an ATmega328P, PIC18F26J11 or Rasberry Pi to an I/O extender and I've attached my current I/O map.
The I2C is a SC16IS750 8 bit + UART I2C expander with an interrupt and reset.
RS485/232 is a mode pin set by DIP switch on a MAX3160 (the half/full duplex pin isn't brought to the RPi GPIO)
The XBee is a common XBee radio, the SPI stuff is for the Bluetooth Bee.
1 Wire is an option, PWM might be handy.
Comments, questions welcome. Don't like the I/O choices; I'm listening.