The Big Ideas that interest me the most concern the organization of society - how we live, how we're taught, and our unformulated thoughts about matters that we tend to take for granted. For the most part, these sites touch on architecture or urban planning. But there's more to it than that, as you'll see.
BLDGBLOG: A collaborative blog, headed by Geoff Manaugh. It's hip tag says it all: "architectural conjecture :: urban speculation :: landscape futures"
James Kunstler's Nastily-Named Site: If you've read Kunstler, a gifted thinker on civic planning and the deleterious doings of developers, this site will be a natural.
The Long Tail: Chris Anderson edits Wired Magazine. He has become intrigued by the operation of power laws on commerce in the Internet Age. A good example of a "Long Tail" business is CaféPress, where the barriers to your selling mugs and T-shirts with your logo on them are minimized, allowing you to make profits on smaller volumes. That's all that I can say without screwing up.
Peak Oil and Gas: Not a cheering site, but persuasive. We're beginning to run out of the stuff.