Algolia’s Magento Search Plugin makes it easy to deliver a lightning fast search experience to your customers.
Product search you can integrate into your Magento store in minutes.
With Algolia's as-you-type search customers think less about how to search and more about what they find. Serve relevant content from the first keystroke.
Highlight popular products for your ecommerce store.
Integrate in minutes – improve search and increase the conversion rate of your e-commerce site.

https://community.algolia.com/magento/

Magento 1

Free Autocomplete and Instant Search Extension

Magento 2

Free Autocomplete and Instant Search Extension