In terms of splattbooks, Wizards has a few options.
1. Race books. It's a no brainer and despite other d20 companies doing it, none of them are "official" so to say so people will buy them.
2. Monster book. Similiar to above but we've heard something about this.
3. Psionic Splattbook: Simliar to Sword & Fist but something like Metal and Mind to detail psychic warrior and psions. More prestige classes, powers, feats, and magic items for them.
Those are the ones I can easily see coming out. We know about some of the other stuff like Dragonlance and I'm sure if Dark Sun is officially coming out, they'll follow the same model and do the first book themselves, although that's not how it worked with Ravenloft.
Genre specific books? Don't see a lot of that as Star Wars coves sci-fi pretty good and they wouldn't want to compete with their own book and Call covers horror pretty well. I'm sure that D20 Modern will offer some options for both those settings.
Unearthed Arcana? Well, the goal does seem to be, in small part at least, a return to 1st edition goods.
Wilderness & Dungeoneer's Survival Guide updates would be interesting as well. Could proof some interesting times as spells, classes, and other default information has gone through some changes.
Fiend Folio? I don't think so since Necromancer is coming out with the good old collection but it'd be nice.
Forgotten Realms will probably get a sourcebook or two.
Adventurers? Maybe one mega adventure.
I'd personally love to see the damned expansion CDs for Dragon Magazine, especially since in this day and age they should be set up for electronic distribution fairly easily. It'd also make it easier to collect and coallate certain things. Hell, a return to the Best of Dragon would be ideal as well.
How about Deities & Demigods II? More divine feats, morei nformation on advancing through divine ranks, creating your own planes (you know, Primal Order level stuff) more divine monsters, etc...
). Right now I'm pretty set. 
