Transferslot - Easily buy and sell side-projects
Product Hunt - A website that lets users share and discover new products
To Build Something - Find side project help and collaborators
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.
Solodoers - Get matched with a side-project you want to scale
BetaList - BetaList provides an overview of upcoming internet startups. Discover and get early access to the future.