A new instance, Zul Gurub, will be opened. It's a 20 man instance, easier than Molten Core and Blackwing's Lair. It's aimed more towards more casual players who haven't been in MC, and therefore it doesn't have as good loot.
There will also be a new Battleground, in Arathi, 20v20, I believe.
And hunter talents will be revised, with a couple of important changes.
The patch will likely be released early september.