Dungeons and dragons has always been rift with campaign settings, both those officially released and those created by DMs themselves. From the grim and dark (metaphorically) Desert world of Dark Sun, to the noble and chivalrous Dragonlance, to the 'classic' settings like The Forgotten Realms, and in more recent times settings such as the Low-magic Eberron, all providing players with ideas, inspiration, and most importantly settings in which to play their games.
 List of D&D Campaign Settings
Council of Wyrms
 Noteworthy/developed 'homebrew' settings Uberstadt
The Unified Setting for /tg/