Real-Time Find and Replace
Set up find and replace rules that are executed AFTER a page is generated by WordPress, but BEFORE it is sent to a user's browser.
Add Search To Menu
The plugin displays search form in the navigation menu which you can configure from the admin area.
Search & Filter Pro – The Ultimate WordPress Filter Plugin
Search by custom fields, post meta, taxonomies, tags, categories, authors, post types, post dates and more - The Ultimate WordPress Filter Plugin with Ajax!
Better Search Replace: A New Plugin for Updating URLs and Text in WordPress Databases