http://www.plymouth.edu/library/opac/ – a WordPress frontend (WP) with a library catalog backend (opac). Although still in development the results look very promising.
Update June 2007
The name of the WPopac project has changed to Scriblio. Also, check out the site for the development partner (Cook Memorial Library) that’s based on Scriblio. Note that this library had no online catalog prior to Scriblio.