A Guide to the Ethereal Plane (AD&D/Planescape), by Cordell, Bruce R.
Hellbound: The Blood War (AD&D/Planescape), by Monte Cook, Colin McComb
In the Abyss (Advanced Dungeons & Dragons, 2nd Edition), by Williams, Skip
In the Cage: A Guide to Sigil (AD&D/Planescape), by Rick Swan, Wolfgang Baur
On Hallowed Ground (Advanced Dungeons & Dragons: Planescape, Deluxe Campaign Accessory/2623), by Colin McComb
Planes of Chaos (Advanced Dungeons & Dragons, 2nd Edition: Planescape, Campaign Expansion/2603), by Wolfgang Baur, Lester Smith
Tales from the Infinite Staircase (AD&D/Planescape Adventure), by Cook, Monte
The Deva Spark (Advanced Dungeons & Dragons/Planescape), by Slasbury, J. M., Slavicsek, Bill