OCLC's xISBN project--finding ISBN's of other editions of a work:

• To use the xISBN service, enter the following URL into your browser window: 
  http://labs.oclc.org/xisbn/[ISBN] (This is not an actual link.)
  substituting an actual ISBN for [ISBN].

• For instance: http://labs.oclc.org/xisbn/0441172717 will pull up all ISBN's of the book
  Dune, by Frank Herbert, as listed in OCLC WorldCat.

• More info on this project: http://www.oclc.org/research/projects/xisbn/