Scarred Lands was the first D&D setting to enjoy really thorough support. It made all the difference for me when I went to the FLGS in Topeka and had a choice between a whopping three books for FR or a stack of books for Scarred Lands. I bought into the latter setting.
Arcanis is, to date, the only d20 setting I've seen which manages to do 'baroque' right. It has a real Vancian feel to it where the actual setting elements are concerned. In fact, Arcanis probably tops my list of favorite d20 fantasy settings.
Dungeonworld, while chock full of typographical errors, is singulalrly unique amongst all published RPG setting ever written (to my knowledge). The idea of an entire world that consists of nothing but dungeon is pretty neat. I wish it had been done up a bit better.
Oathbound was, for me, the closest thing to Planescape that I ever saw get any kind of real support for D&D 3x. It is a well-written, artistically stunning, product line - that apprently a lot of people just plain dislike for varying reasons (I admit that the 'only for higher level characters' bit turned me off).