They've stopped doing the 'old style'. There isn't 'player's handbook 4' or 'adventurer's vault 3' coming out, etc.
The Monster Manuals seem to be going the route of Monster Vault: Subtitle. They come in a box with tokens, thus the 'vault' concept, I guess.
There is a new item book coming in the future, but it's titled Mordekaiden's Emporium, or something to that effect. Again, it's functionally equivalent to an Adventurer's Vault, but meant to have more flavor/story, etc.
Instead of another X Power book, there is going to be Heroes of Shadows, which will feature support for multiple classes (so far, a new build for paladin's and new wizarding schools have been confirmed, although there should be more). So, it's similr to the old power books, but focussing on a theme (dark magic, undead, the shadowfell, etc) instead of a power source.
There is going to be a Heroes of Sword and Spell which updates/reprints stuff from Player's Handbook 1 in addition to including rules on how to mix and match with Essential builds (multiclassing and the like). There is also a Heroes of the Heroic Tier book which seems to be introducing new options (professions, themes, etc)
There's also a Neverwinter campaign setting coming up, etc.
Most of that stuff is all in the new year. The Essentials branded stuff pretty much runs out. Specifically, Essentials is going to be defined as the books that the book store is supposed to always keep in stock, while newer content which may or may not be formatted the same way as Essentials products [I don't know how many hardcover books we'll be seeing anymore] would be treated like most of the older products ... which is that most places will likely not reorder if they sell out unless someone special orders it.