Two books are coming out this year.
The first is Tomb of Annihilation, an adventure that takes players to an area called Chult (not part of the until-now standard 5e setting of the Sword Coast, though it is still in Faerûn) where the demilich from the infamous Tomb of Horrors is performing all sorts of nasty deeds, eating away at resurrection magic to fuel his undead. The adventure is going to be filled with dinosaurs, zombies, and zombie dinosaurs, and presumably the eponymous tomb, which we can expect to be a real death-trap.
The other book actually excites me a lot more, which is Xanathar's Guide to Everything. Just as Volo's Guide to Monsters was theoretically written from the perspective of a character in the Forgotten Realms, Xanathar is a beholder crime lord in Waterdeep. This book will be an expansion of rules, worked out in the Unearthed Arcana articles but now pinned down in official forms.
I've gotten way more use out of Volo's than any of the adventure books I've bought, and so I think Xanathar's will be a definite purchase. This includes new and expanded rules systems, but also new subclasses for every class (possibly with the exception of the Wizard, but they've got to have the most already, right?)
Anyway, I'll be following these releases.