Klevu - Klevu offers instant site search solution for eCommerce stores.
V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.
Adobe Audience Manager - Adobe Audience Manager is a data management platform that integrates online and offline data to deliver a unified view of all your audiences
Algolia - Algolia's Search API makes it easy to deliver a great search experience in your apps & websites. Algolia Search provides hosted full-text, numerical, faceted and geolocalized search.
Google Audience Center - 3 votes and 6 comments so far on Reddit