BuiltWith - Find out the technology behind websites
SalesOptimize - Selling to online retailers? Revolutionary sales lead generation search engine driven by deep web analytics
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
hubsell - Sales automation for modern sales teams
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Elucify - A completely free software tool that uses crowdsourced data to find business email addresses