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.
Product Hunt - A website that lets users share and discover new products
Sites Like - Siteslike opened it's doors to the public on the 4th of december in 2008, since that time...
moreofit.com - Moreofit is the first (and best) website similarity search engine.
FreeSitesLike - FreeSitesLike is a user contributed website dedicated to offering its visitors with plenty of options to a specific website.