Reddit - Reddit gives you the best of the internet in one place. Get a constantly updating feed of breaking news, fun stories, pics, memes, and videos just for you.
Hacker News - Hacker News is a social news website focusing on computer science and entrepreneurship. It is run by Paul Graham's investment fund and startup incubator, Y Combinator.
Contextly - Contextly provides content recommendation system for publishers.
4chan - 4chan is a simple image-based bulletin board where anyone can post comments and share images.
Digg - Digg delivers the most interesting and talked-about stories on the Web right now.
Snapzu - Snapzu is basically reddit alternative.