My company has created an excellent solution for OPACs (Online Public Access Catalogues) that is faster, more user-friendly and more comprehensive than any other that we're aware of. For more information see our presentation at Opac Online. Best of all, Opac Online is open source and leverages the power of Lucene, the state-of-the-art information retrieval component. We offer cool features such as a "Did you mean.." function if your query returns too few results, a autocomplete-as-you-type search for thesaurus terms, and much more. Typical queries (even wildcard queries) yield results in less than a third of a second, using catalogues that have 100.000+ records !
Our address is opaconline.com. Please give us your comments and feedback and help us build the world's best solution for librarians and other library users !