I want settings and environments that are not well (or at all) supported by WotC. Aquatics, both seafaring and underwater. 3D combat aids for flying or underwater battles. Terrain-specific or genre-specific ecologies and cultures, and adventures set in them, with just enough crunch to make the flavor stand out. Some specific settings:
An urban political morass - Medici Florence meets Byzantium as done by White Wolf
A military campaign book - constructing a party as a military unit, with rules for sieges, artillery, skill challenge examples for leadership and tactics, etc.
Rules and ideas for a total wilderness or stone age campaign, where players must make or find everything. Not just no magic shops, but no civilization at all to fall back on.
Fantasy versions of interesting mythical or historical settings. Pharaonic Egypt, Three Kingdoms China, Aztec and Mayan empires.
An occasional feat or power in these is OK, even though it won't fit in Character Builder, but not a whole build or paragon path.