Search & Filter is a simple search and filtering plugin for WordPress.
At its simplest you can produce a search that allows you to filter tags and categories:
you add a shortcode like this:
[searchandfilter fields="search,category,post_tag"]
and get this:
The Search & Filter Free Edition Documentation gives more complex examples for example:
[searchandfilter fields="search,post_date" types=",daterange" headings=",Post Date"]
[searchandfilter fields="search,post_types" post_types="post,page" headings=",Post Types"]
