Bill developed an Arduino library for PlayStation 2 controllers:
I had to rewrite a lot of code that powers the library, there is not much left of the original code written by Shutter of Arduino forums. There were many bug fixes, now the controller should automatically be in analog mode, and the mode button should be locked. There’s also a catch to make sure not to much time has past since the last controller reading. If there was, it will configure the controller again, in case it timed out.