Domcomp - No-nonsense domain price comparisons, updated daily
BuiltWith - Find out the technology behind websites
dofo.com - Domain search platform Dofo.com gathers all registered (350 million) domains of the world in a single place. Dofo also brings together all the domain names that are on sale, provides useful features, all completely free.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Pricepeek - Compare prices of the same product across all Amazon locales
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.