Something Bad Happens) when I had something approximating an idea (though it has probably been tried before). For those nights when no one wants to GM, the group chooses what rules-system they want to play. Then everyone gabs their own adventure module. If people are comfortable adapting a module from a different game, or setting, or scaling up/down from a different level module, so much the better!
One player goes first and is the GM for that round. He describes the entrance to his 'dungeon' and runs any encounters. Then the party moves inside and the next player is now the GM and she describes a room or corridor from her module, running any encounters ... and so on.
Wanna get weird but don't want to jigger with the rules too much?; go with a D&Dmash; use a Dark Sun/Starjammer/Planescape/Forgotten Realms mash. Wanna go a little weirder? Open up to anything! Personally, I'd I'd love to play an All Flesh Must Be Eaten/Shadowrun/Paranoia!/GammaWorld mash.