Sites Like - Siteslike opened it's doors to the public on the 4th of december in 2008, since that time...
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.
moreofit.com - Moreofit is the first (and best) website similarity search engine.
SimilarSites - Easily find more sites like those you like.
Product Hunt - A website that lets users share and discover new products
Similar Site Search - SimilarSiteSearch helps you find similar, related, or alternative websites.