I’ve been reading Big Think for a while now, and it’s always pretty interesting. Perhaps their most thought-provoking articles are in the Dangerous Ideas series, which they describe as:
Brace yourself: these ideas may at first seem shocking or counter-intuitive—but they are worth our attention, even if we end up rejecting them. Every idea in this blog is supported by contributions from leading experts, from the world’s top theoretical physicist Stephen Hawking, to Nobel Prize-winning economist Gary Becker, to linguist and philosopher Noam Chomsky.
It’s worth a look. Some are definitely better than others, and none really explore the issues in much depth, but in general they’re good to get you thinking or to start a conversation. A few of my favorites:
Blendor 
I recently came across Big Think by way of a couple videos Penn Jillette did with them (e.g. http://youtu.be/WvaZwPPd7m0) and I really liked the idea. I’ll check out more of their articles.