OCLC has xISBN, of course. And LibX, the incredibly useful Firefox extension, uses it. If you’re looking at one print manifestation and you know its ISBN, it’s the easy way to get to other manifestations of the same work from your library. (LibX also does much more. Check it out if you don’t use it already.)
Tony Hirst posted Looking Up Alternative Copies of a Book on Amazon, via ThingISBN, wherein he shows, with snazzy graphics, how he uses Yahoo Pipes (which is a really impressive piece of work, and fun to use) and LIbraryThing‘s thingISBN to do something similar.
He spoke about it at Mashed Libraries 2008 and Andy McGregor wrote Mashing thingISBN and Library Lookup Using Yahoo Pipes Courtesy of Mashed Libraries 2008