Many libraries have begin to add dynamic linking from item records in their online catalogs to corresponding information on WorldCat.org. By using a URL syntax that builds a WorldCat link on-the-fly around an ISBN, ISSN or OCLC Number, their OPACs give a user the option to search other nearby libraries when an item is unavailable locally.
The Santa Monica Public Library has implemented the linking solution described above: Each item record in its Web catalog includes a "Check nearby libraries" WorldCat link (right) which is dynamically generated using the ISBN for the displayed item. SMPL's implementation of the syntax includes geographic limiting by the library's postal ZIP code, so the WorldCat page reached via the link presents results that start with libraries in neighboring communities.
Here are some of the libraries that have integrated dynamic WorldCat links with ILS systems from popular vendors. Visit their sites to try a search and see these links in action.