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.
V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Lotame - Make your data actionable, learn about your most valuable customers, improve ROI by targeting the right audience and increase relevance across screens.
Site Search 360 - Site Search 360 enhances and improves your built-in CMS or product search with autocompletion, semantic search, filters, facets, detailed analytics, and a whole lot of customization options.
Google Audience Center - 3 votes and 6 comments so far on Reddit