"This might seem to be a strange advice for a Dungeon Master Guide, but it's entirely possible to play D&D without a Dungeon Master. If you're all looking for is fun and exciting combat, with no more than the barest hint of plot or purpose, a random dungeon with a random encounter deck is all you need. Someone needs to prepare the deck and someone needs to run the monsters during the game, it doesn't have to be the same person. All the players can decide together what the monsters do, and let the player who's the target of an attack make the attack roll (or have the person to the left roll for the monster). [...]" -4th Ed.