At Algolia, we've been working for the last year to create the best search application for Shopify, and it's just been officially released! We're providing an instant search experience (results in less than 100ms at each keystroke), with typo-tolerance, synonyms and analytics. It handles realtime updating of your search, metafields, and the whole code installs in your theme, meaning you can customize everything.
Why should you care? Because an awesome search on your site will boost your conversion and retention rates!
We have a few links for you:
Let us know what you think!