Here's a great list of interoperability and integration resources on the web. Some of these are well know, some are a gem just waiting to be discovered. Some are great books about integration and enterprise patterns you should be reading when dealing with these issues.
I got the list off of an email that represents an exclusive course that will take place next month. It's a pretty closed registration, and the list you see here is simply the prerequisite list for this course :). So I said to myself "well, we can at least learn what we don't know from this list..."
I checked some of this out and it's great stuff, so I decided to put all of it in one place for future reference: