Today's new releases take us back to the worlds that were the cradle of D&D.
Dave Arneson's supplement to Original D&D is now out (again). Blackmoor gave us the first ready to run adventure published by TSR, Temple of the Frog, the Monk and Assassin classes and the often forgotten D&D to hit location system.
In later editions of the game Blackmoor would appear in both the World of Greyhawk and the Known World of Mystara.
The D&D Gazetteer for 3e came out as soon as 3e did and established that Greyhawk as the default world for D&D 3. It was quickly eclipsed by the Living Greyhawk Gazetteer, but both had really nice poster sized maps.