My wife and I have been privileged to attend 4 of the past 5 Catalyst conferences in Duluth, GA. This past October, one of the main stage speakers was Seth Godin, who gave a fabulous presentation based on the concepts he explored in his latest book Tribes. (He then proceeded to give everyone in the audience a free copy of the book!)
Seth is always worth listening to. Here's a video provided by TED (by the way, one of the most helpful Internet destinations I've found).