Dayton AMA

If you can only read one Marketing related blog, besides Dayton AMA of course, it should be Seth Godin's blog. I find something great on here almost daily. Check out his take on Managing the Vague. If you do anything today, get an RSS feed and subscribe to his blog, and Dayton AMA too. I guarantee that you will have a high marketing ROI for your time and efforts.
Seth's Blog: Managing the vague