so... who's your circle of eight?
All good campaign settings, but you just cannot beat the classics. The world of Greyhawk was the first campaign setting to be fully fleshed out (Blackmoor wasn't half as complex), and was the brainchild of Gary E. Gygax, founder of D&D. The setting was like FR in the fact that it had every terrain feature, plenty of deities, allowed many options, and was a very classic Tolkien-style setting. It differed (and was better, in my opinion) by being much more gritty than the sometimes flowery Forgotten Realms.
Of course, anyone who reads my name will realize I'm sorta biased on this.
Runner-ups would be Dark Sun, Forgotten Realms and Ravenloft.
Well, as one may assume, I like Blackmoor. Somewhat.
After that, I guess, at this point, Dawnforge and Ravenloft.
My favorite was the one that didn't make it for over a year or two: Red Steel. Swashbuckling Zorro-type setting with superpowered adventurers? I'm all for it.
Though it was part of Mystara, so I suppose my vote would then go for Mystara. The Savage Coast, a wondrous land of magic, a brutal land of gladiators, a hollow earth to explore, immortals instead of gods, and one of my favorite monsters: the thoul. Awesome.
I love Birthright, my favorite setting of all time, We played a long campaign which was very game of throne like, it ended when the players thought they could take on the Gorgon, well that didn't go so well. The setting just had what I liked, low magic (not very common) lots of cultures, just a great all around setting.
Forgotten Realms, because I've played it the longest in 2nd,3rd,3.5 eds. Points of light in 4th both Kaewin and I enjoyed it.
Elves keep their counsel and sharpen their ears.