After a bit of delay, here's the last settings I meant to cover. Some of them are iffy---not D&D settings at all, but d20 settings that are really meant for slightly different games. But what they hey; this is my last post on the subject, so I figgered I'd go all out.
Freeport: This is one of my favorite d20 settings, although ironically the in print and best Freeport book is system neutral and could be used for any system (there are, in fact, companions designed to "port" the setting into d20, True20, Savage Worlds, and Castles & Crusades, as well as a blog post at publisher Green Ronin that gives some suggestions on using Warhammer Fantasy Roleplaying.) That said, the setting is pretty iconically D&D, and obviously so, even though it doesn't have any system. The setting assumptions have elves, halflings, gnomes, dwarves, orcs, goblinoids, etc. and the presence of arcane magic users and clerics who perform their roles exactly as in D&D are inherent setting assumptions.
What I really like about the setting is that it very successfully ported D&D into the Golden Age of piracy. It did away with simplistic notions like alignment, and is pretty gritty, dirty, and yet still very interesting and fun.
Dragonlance: This was licensed and published by Sovereign Press, which is the company of (among others) Margaret Weis, co-creater of the setting in the first place. Decent setting. It always struck me as more appropriate for novels than for gaming; but I could be biased by the terrible earlier modules that were published by TSR back in the day. In any case, the setting has the annoying tendency to "blow up" regularly and get completely rebuilt from scratch. It's got some notable differences from "default" D&D, but bizarrely, rather than being a help, it's a bit of a hindrance in this case, in my opinion. The setting is too D&D to accept these differences with good grace.
Planescape: Maybe I'm cheating a bit by including this one. Technically, it hasn't been published, but in actuality, Planescape was pretty much folded into the core setting (it was also originally built on the core setting back in the day, too) so a number of core books get pretty close to recreating the setting in a 3e milieu anyway. I like it. It's wide open and somewhat crazy, but it pulls that vibe off with panache.
The Wheel of Time: One of the first alt.D&D's built off the d20 engine, the Wheel of Time game is the setting for the Wheel of Time book series, naturally. This is another one that has some interesting things about it, but isn't a good setting to use for gaming. The big story's already being told in the novels, obviously, and the heroes of the novels are the heroes of the story. That makes using the setting difficult. Add to that that the author is, again, "blowing up" the setting and rebuilding it as he goes, and the setting has some things that are worth borrowing, but it isn't a good one to use as is.
Star Wars: Now I'm really far afield, but this is a favorite setting of mine. It's pretty wide open, if you remove your game from the events of the movie somewhat. I like moving it forward a few hundred years in time, but the Knights of the Old Republic video game proved it could be done moving backwards a few thousand years too.
Traveller: Again; a not-D&D setting, and the "T20" book doesn't actually have much setting in it, but it's a fun setting. Another "wide open" one that actually encourages an awful lot of GM creating, and gives you good tools to do so.