Replace your sluggish and rigid SQL search with the world open source leader Apache Solr wich powers the leading internet websites
Scriblio enables faceted searching and browsing of WordPress posts, pages, and custom post types.
Powerful AJAX-based search alternative which supports faceting queries by taxonomies, terms, location, and post metadata.
Site search functionality for WordPress powered sites. The plugin is based on powerful hosted ElasticSearch engine (hosted for free)