I have high hopes for the upcoming Monster Vault (Threats to Nentir Vale), as marketing blurbs have suggested some "old classic" monsters. I would be indescribably thrilled if we see some Basic/Expert types such as: decapus, thouls, various giant beetles/lizards, phanaton, aranea, living statues or magen, new werecreatures, etc.
But while I like the Nentir Vale, I'd like to see more "sandboxes" from the core world. I'd like to see a warmer setting, a coastal region, a desert... There are lots of cool things that simply have no place in the Nentir Vale (snake-infested jungles, back alley fights with pirates, etc). The geography is very limited, currently.
Of course, if too much is developed about it, it turns into another Forgotten Realms... perhaps minus 1 archmage in each town but still...