Open Grave (book of undead?) Lots of new monsters, that's a no-brainer...some special focus on Vecna, that's kind of fun. Undead oozes? Uh...This is more a DM's resource book with very little player focus, moreso than any previous book. *sigh* So, no necromancy for my character right now. A few rituals which might be useful to players. More "color text" than before.
Stronger tendency as a design strategy to seperate Player books from GM books, which might impact sales a bit, but players won't need to buy quite as many books as last time...
Monster Manual II in production. About time...Not listed in the catalog, tho, so I assume this (and Vault II?) are coming out next summer or later. This is a big assumption. The text for Vault II is written already, so maybe they'll advance that one more quickly.
PHB II - Swordmage will not be reprinted in PHBII (that's not very interesting, but it's information of some sort...no reprint material.) However, there's supplemental material Arcane Power for the Swordmage. New build for Swordmage, apparently, in Arcane Power. Possibility of a Necromancer build for Arcane Power? Hmm. No martial classes in PHB2. Extended rules for Polymorph-type effects will be included in PHB2, tho (probalby because of the Druid class...)
Arcane Power - No new classes (only in PHBs and campaign settings).
Eberron next setting book, Dragonlance pretty likely to be next...maybe Ravenloft next?
Upcoming "digital initiative" for Forgotten Realms - villians, societies? New content for various settings will PRIMARILY be released in a digital format (Dungeon, Dragon), to keep the sourcebooks down to a minimal number.
Additional sourcebook releases (as of Gencon:)
5/19/09: Monster Manual II
July 2009: Divine Power
August 09: Adventurer's Vault II