I found a terrific resource yesterday while browsing stacks at Barnes and Noble. Its a paperback by Bill McMillon (et.al.), VOLUNTEER VACATIONS, 9th edition, 2006. Although the focus is broader than just those volunteer organizations which include diving components, it is relatively easy to research those under a category they call "Natural Conservation (sea)." The authors include over 150 organizations and for each they succinctly describe the type of project, yr. organization was founded, number of volunteers last year, the work they do, their project locations, times when projects occur and their length, the costs, the specific skills required, and how to get more info (websites, telephone numbers, email addresses etc.) I have never actually joined any organization that combines diving with ecological research (etc.) but browsing this book has got me really excited: I've bookmarked 15 organizations to investigate further. If you have questions, feel free to write me.