DragonLancer
Adventurer
There's a big thing about getting players to be Dungeon Masters, but I've always felt that once a player sees what is going on behind the curtain, it ruins the player enjoyment. I think it's better for players to not know.I know for my own part that once I started DMing and got to know the ropes, playing became a bit less fun as I'd seen (and couldn't unsee) what went on under the hood and thus much of the mystery was gone.
I find running games for players who have never GM'd a game is a much better experience for me. There is a wonder to the game and in their experiences which is lost once they see how the game runs and when they see monsters reduced to a set of numbers and abilities.