AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
SimilarSites - Easily find more sites like those you like.
Sites Like - Siteslike opened it's doors to the public on the 4th of december in 2008, since that time...
Product Hunt - A website that lets users share and discover new products
SimilarWeb - SimilarWeb.com is a website analysis tool that gives you analytics information for any website.
Similar Site Search - SimilarSiteSearch helps you find similar, related, or alternative websites.