Of all the content you've ever seen from Dragon Magazine or Dungeon Magazine, what really stood out to you? I'll go first:
- The various features on different famous/infamous beings of the multiverse were always a treat. I loved the Demonomicon of Iggwilv series, and during the 4E era I especially enjoyed the various additional series introduced dedicated to other kinds of beings: Deities & Demigods for the gods, Codex of Betrayal for the devils, Lords of Chaos for the primordials, and Court of Stars for the archfey. Of all the Dragon Magazine features I think I miss those the most.
- The two adventure paths that really got into extraplanar content were gems. The Savage Tide took me on a tour of the lower planes, especially the Abyss, and Scales of War had a raid on a githyanki naval base in the Astral, intrigue in the City of Brass, and a final dungen crawl through Tiamat's inner sanctum.
- One Dragon Magazine article I remember featured a selection of charms and other materials intended for commoners and fledgling adventurers to use against various supernatural threats. Another I was found of had a selection of unusual beverages, and another listed a number of demiplanes mentioned throughout D&D history.