From paizo:
Today, Wizards of the Coast and Paizo Publishing announced the conclusion of Paizo's license to publish Dragon and Dungeon magazines. The magazines will cease publication following the release of the September issues, which ship to subscribers and newsstands in August. The final issues will be Dragon #359 and Dungeon #150.
Wizards of the Coast will be moving the kind of content currently found in Dragon and Dungeon to an online model. Both companies remain on good terms and continue to discuss future opportunities for publishing partnerships.
I hate to see this happen. Back when I first starting playing D&D this magazine was as important as the rules. You had to read it. I guess I can't really complain, I haven't picked up an issue since the 80's. It's still a bummer to see the magazine come to an end.
