I've been meaning to point to openadaptor.org for a while. Maybe I did, I can't remember.
I wrote an openadaptor-like system last year for a customer of OAAI. It was very cool (IMHO) and openadaptor is too.
The system I wrote is becoming more and more central to their systems. If you're looking for a way to integrate your systems, take a look at openadaptor.