Product Hunt - A website that lets users share and discover new products
PitchWall - Browse new startups, and submit your mobile app/games startup's beta page here.
Betafy - Where startups meet beta users!
BetaList - BetaList provides an overview of upcoming internet startups. Discover and get early access to the future.
Beta Family - 50,000 testers to test your app
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.