Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.

Elucify - A completely free software tool that uses crowdsourced data to find business email addresses

BuiltWith - Find out the technology behind websites

KiteDesk - Use KiteDesk sales prospecting software to generate leads from our premium data marketplace. Then reach prospects and build a sales pipeline with organized Lead Lists. Syncs direct with CRM too!

PublicWWW - source code search engine

WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.