I have set up a highly experimental (read: pre-pre-alpha) tool on the toolserver to search for combinations of key/value pairs in templates. Like TemplateTiger, but for the live site (one day...)
URL: http://toolserver.org/~magnus/knights_template.php (as in "Knights Templar", sorry, couldn't resist)
What does it do (or should do): Find actors on Wikipedia that have a book by publisher McFarland cited as source? No problem: http://tinyurl.com/chadva (will take a few seconds)
All templates used on [[Roy Scheider]], with key/value pairs: http://tinyurl.com/dkpbh7
Things that need fixing (like, everything): * Slooow * Only en.wikipedia * Only 16K pages indexed at the moment (some Recent Changes snapshots) * Only templates used directly in the article are indexed * Needs continuous update (can run on cron, but disabled because text retrieval and DB storage too slow to keep up with RC) * Needs better query interface * Might cause database size problems
All in all, it would be much better directly integrated into MediaWiki (no need for text retrieval/parsing, no bulk updates). But I've been saying that for years, at least this is a first attempt.
Cheers, Magnus