F5Bot - F5Bot will send you an email whenever your brand, product, or keyword is mentioned online.

mention - Media monitoring made easy with Mention. Create alerts on your name, brand, competitors and be informed in real-time of any mention on the web and social networks

KWatch.io - Monitor Keywords on Reddit, Twitter, Linkedin, Quora, Facebook, and Hacker News. Receive an instant alert when specific keywords appear on social media.

SOCIALHOSE.IO - Discover an enterprise social listening platform that enables brands & agencies to monitor the web & listen to their audience, built to scale. Start for free!

Syften - Better social media keyword alerts

Google Alerts - Google Alerts will send you email or RSS updates of the latest relevant Google results (web, news...