The HathiTrust BibAPI might help you out -- you can get MARC-XML back with
a call, although of course its only as good as the underlying record and
our coverage won't be nearly as good as the OCLC.

Format is:

On Tue, Jan 22, 2013 at 8:38 PM, William Denton <[log in to unmask]> wrote:

> On 21 January 2013, David Fiander wrote:
>  All I'm really looking for at this point is a way to convert an ISBN into
>> basic bibliographic data, and to find any related ISBNs, a la OCLC's xISBN
>> service.
> LibraryThing's thingISBN is nice and might serve your needs:
> Bill
> --
> William Denton
> Toronto, Canada

Bill Dueber
Library Systems Programmer
University of Michigan Library