Hi Brian,
First step would be to collectively as organization decide what should be your system of records, before other systems take a copy. Also decide what data from other system will be exception in overwriting the main system. To give you an example, sales can be the contact's owner in CRM, but event registration data about the contact can be owned by marketing.
Once you establish the above, next step would be to come to an agreement on data standards. I would recommend following some of the techniques discussed here.. http://topliners.eloqua.com/docs/DOC-2401.
At least something for you get started on your thoughts and how you want to proceed further.
Thanks
Amit Pandya