Mattermark - Ranking 800,000+ high growth Internet companies
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.
Breakout List - A list of the fastest growing startups
Top Similar Sites - Top Similar Sites helps you find similar, alternative or related sites to any website instantly.
Crunchbase - Crunchbase is a platform for discovering industry trends, investments, and news about companies around the world.
Growing Page - Browse web projects and evaluate them by multiple criteria.