NCSU North Carolina State University OPAC at http://www.lib.ncsu.edu/catalog/ uses Endeca instead of a library vendor opac.
Informative search results screen features: narrow by lcsh subheadings and types (General works, etc..), link to similar items, the floor of the building where item is located, checkout status, sort search by "most popular" etc...
Some things are still powered by the SIRSI backend, like authority search and full display.
The main disadvantage, and it's a big one, is that information is updated from SIRSI to Endeca daily, so may be up to 24 hours out of date, including circulation status (!)
February 2009 issue of Computers in Library has an article called Creating Open Source Conversation about Darien Library's website, which integrates the ILS with the website very nicely using Drupal and SOPAC 2.0. full article: here
OPAC Vendors We Like
If you would like to recommend a vendor, please sign your name to the recommendation so that we know it's not from a vendor. An explanation of why you like this vendor would be great too!
I haven't used Aquabrowser first hand, but it's worth looking into. It's a user interface that sits on top of an existing library catalog. Users search the online catalog and get results in visual form (a "word cloud"). If you've used Kartoo, you'll see a similarity. The results show associations, including shades of meaning and related spellings. Ellie
There are many products that can enhance your OPAC. Here is a list of them. Please add to this list if you know of any:
- LibraryThing for Libraries (Sample implementations)
- Scriblio (formerly WPopac) is a free, open source CMS and OPAC with faceted searching and browsing features based on WordPress.
-  Millennium Integration module for Drupal, crawls/imports items from III WebOPACs into an existing Drupal site. You can then use the enormous variety of Drupal modules to build applications like a Discovery Layer, book recommendations, a union catalog, etc.
Blogs/Websites to Watch
Lorcan Dempsey -