Relevanssi - Relevanssi replaces the standard WordPress search with a better search engine, with lots of features and configurable options.
FiboSearch - Give your WooCommerce users a fast, convenient and relevant autocomplete search and save them the effort
SearchWP for Firefox - Jump-to-word buttons and highlighting for the search box content
Advanced Woo Search - Advanced Woo Search - WordPress ajax search plugin for WooCommerce store. Search in product title, description, excerpt, sku, tags, categories, attributes, custom fields, custom taxonomies.
Swiftype - The simplest way to add search to your website or application. Sign up for free.
Ajax Search Lite - WordPress Live Search plugin - Ajax search lite. A responsive live search engine for WordPress, for free.