The Lendore Isles....the real ones, from before they were taken over by elves by the time of Out of the Ashes (I have no idea why that was done, perfectly good little corner of the world away from the madding crowd....did someone have something against Lenard Lakofka?). Secret of Bone Hill/Assassin's Knot/Deep Dwarven Delve are an excellent basis for a campaign.
Either that, or Blackmoor. Frederick Weining's writeup of the place in Oerth Journal, transplanted to the Gazetteer, is pure quality. It's also an ancient and mysterious place, what with black ice on the doorstep, the old magic infusing the land which keeps Iuz at bay, and quirky bits and pieces from Arneson's Blackmoor, such as the Egg of Coot.