Category Wise Search
Category Wise Search Widget plugin.You have option search specific category content.
Plugin Tag: search by category
Product Category Dropdowns
Displays product categories as dependent drop-down selects.
Swiftype Site Search Plugin for WordPress
Fast, intelligent, and fully customizable search for your site.
Advance Ajax Live Search
Search By Author-Tag-Cats-Date And Keyword.
Keyspider Site Search Plugin for WordPress
Relevant, intelligent, and fully customizable site search for your WordPress website.