A few people have mentioned Jakandor, which is one of my favourite 2e settings. It really had a certain SOMETHING to it. Funny thing, though, relatively few people actually have copies of it (sometimes it's actually hard to find even on eBAY).
The general idea of the game, though (Wizards vs. Barbarians, humans-only, in an isle of dread-like jungle island filled with ruins) is one that I'd love to see. But, truth be told, I think if we ever saw a new Jakandor (which isn't likely), it'd be in the (web)pages of DRAGON.
Funny story, a few years ago when DRAGON released the classic settings issue for the first time, they wrote about material for D&D settings that they couldn't include in the magazine, and they talked about Jakandor. The funny thing about it is, they named the wrong cultures and generally got the world mixed up. I figure, if even the D&D gurus over at DRAGON don't know much about the setting, it probably failed miserably.
Unfortunate, but true.
Anyways, my list:
1) Dark Sun. I have a feeling we'll see a 4e Dark Sun (the 3e Dark Sun DRAGON/DUNGEON issues were great sellers, if I recall). Whether or not it's as good as 2e Dark Sun, I don't know. I have a feeling it'll be even better, since I liked the direction the Dragon DS went - advance the timeline, destroy the metaplot, and make things "dark" again. I think a wotc version of it would be cool, but I don't know if I want to see the equivalent of Half-Giants and Thri-Kreen with LA.
2) Jakandor: I mentioned it above, and I believe what I said, but a part of me would still love to see this setting get the attention it deserves. But I'd settle for a three-part series in DRAGON (much like the original setting - one book for the Knorr, one for the Charonti, and one book describing adventures on Jakandor).
3) Council of Wyrms: A great idea for a D&D game world, and since they claim to be making Dragons easier to run now, I think it might be a viable option for players. High Power games, political games, and even dungeon crawls (if you send your draconic "familiars" in) could be supported. It was a cool idea, it really was.
4) Spelljammer: Just oddball enough that I think my group would enjoy it.
5) Planescape: I think we'll see a 4e planescape again, too. But then, we might not, since Planescape sort of requires the Great Wheel, which is getting ousted in 4e. Unfortunate, but there it is.