Hey, two great observers of online culture are Dave Weinberger, who I've thanked before and Howard Rheingold.
Dave is one of the authors of the Cluetrain Manifesto, which helped me understand what I was seeing of craigslist community, which led to doing a much better job. He's got a lot going on here.
Howard is one of the great observers of online community, writing the seminal The Virtual Community and now smartmobs about how technology is transforming.
I highly recommend the work of both guys, they really have helped out and influenced me: