Mattermark - Ranking 800,000+ high growth Internet companies
PitchWall - Browse new startups, and submit your mobile app/games startup's beta page here.
Breakout List - A list of the fastest growing startups
Product Hunt - A website that lets users share and discover new products
Crunchbase - Crunchbase is a platform for discovering industry trends, investments, and news about companies around the world.
SimilarPages.com - SimilarPages has found and classified millions of interesting sites hidden due to low popularity with the goal of helping you discover and search a larger portion of the web