So, I'm personally looking to lean between the Mad Laboratory and "Ryl'yeh". I think both of them would make for an awesome adventure setting, way too many options as a GM/DM and really engaging environment to play in (if you have the playgroup that is willing to immerse, otherwise any adventure is about equal to "hey guys, how about you fight what's on page 114 next...")

Mad Lab: Because I LOVED the story about the insane surgeon (and based a D&D Dungeon/NPC on that precise character).
Ryl'yeh: Because seriously, how much fun would it be to have a map of the near-famous sleeping place of Cthulhu? (Cthulhu not included, requires 2xAA battery)