Free version is very nice, Pro version is even better!

This is another plugin that should be standard in WordPress, at a minimum for all post types with archives. This plugin makes it very easy to build perfectly functional and easy to use filters and AJAX search boxes for nearly any custom post type. The only filter I have problems with are for those with future dates – i.e., upcoming events. This plugin is just not suitable for that purpose, but it works great for everything else!