Kings of Dust and Bone
The bard, monk, and paladin classes do not exist in Dark Sun. Other classes have the following modifications.
Clerics must choose from one of the following four domains: Life (Water), Light (Fire), Tempest (Air), or War (Earth).
Druids with the Circle of the Land subclass are limited to the desert, forest, or mountain circles.
The sorcerer class has been converted to “psion”; its spells are considered psionic rather than arcane. (This will change if official or semi-official psionic rules ever appear.) Psion spells do not defile.
Warlocks can only choose the Great Old One subclass to represent power derived from a Sorcerer King. So long as the warlock remains faithful to his or her Sorcerer King, her magic does not defile, instead being drawn from the arcane wellspring of that creature.