My campaign's medieval Europe with a heavy, heavy dose of D&D fantasy injected into its veins. As I'm fond of saying, the campaign setting has more supplements and sourcebooks than anything ever published ever.
However, I play loose with history; it's really just a backdrop that I put up behind the vict- er, players. I don't even know what century I'm running in. And I made magic analogous with technology, which means no fireballs until the Renaissance. Or the PCs go to China.
For more info, I'm currently journaling the campaign as a webcomic. People seem to like it.