Dark Sun was a fun setting, but I always thought that the #DnD rules were an awkward fit. The wild psionic powers, the differences in available equipment, the transhumanist spellcasters... it all diverges pretty strongly from "standard" D&D.
I once ran a #GURPS with it, which I thought was a pretty good fit - using tbe system from GURPS Psionic Powers, and giving each character 25 points from one of the prepackaged power sets. It worked pretty well.