Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.
BuiltWith - Find out the technology behind websites
Albacross - The world's first free B2B Lead Generation Network. Albacross help companies master their B2B digital marketing with Lead Generation and targeted marketing
TechsFound - Find Running Technologies on Website
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.