The Flamenco Search System project is exploring how to best create web-based search interfaces based on faceted thesaurii. The demo inteface they have built for an architecture image collection is excellent. It allows the user to triangulate a set of results by selecting terms from multiple facets. This triangulation allows a user to quickly narrow down to a small set of specific records even within a large overall set of records.
The site also has several articles that give the background on how they created their design.