Arduino resources:

Tutorial for input shift registers used on arduino : http://www.arduino.cc/en/Tutorial/ShiftIn

Tutorial for output shift registers used on arduino : http://www.arduino.cc/en/Tutorial/ShiftOut

Thread about pduino/firmata and pots connected to an arduino: http://puredata.hurleur.com/sujet-2347-pduino-controlling-sound-over-potentiometers

Message board thread about pduino, looks like a board that Hans, creator of pduino haunts: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1148420030/7
also, same board, different thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1148554125

A nice looking blog about physical computing and coding: http://www.tigoe.net/pcomp/code/

Beginners hookup tutorials for arduino: http://www.ladyada.net/learn/arduino/starterpack.html

Firmata, a communication protocol and firmware for arduino: http://firmata.org/wiki/V2.0ProtocolDetails

PD Objects, this pd module with firmata gives us low level access/control of the arduino pins: http://at.or.at/hans/pd/objects.html