r/DnDBehindTheScreen – The most valuable DnD source of information on the net!
r/DMAcademy – For general DM questions.
DndAdventureWriter – Fine tune your adventure ideas with the help of others.
r/DMToolkit – Place to find and share DM tools. We are not affiliated with this subreddit, but highly encourage you to check it out!
r/d100 – Lists of all kinds of things. Great to use for inspiration or the fly while playing.
r/BehindTheTables – Random tables!
r/worldbuilding – World building subreddit.
r/battlemaps – Find and share battlemaps.
r/UnearthedArcana – For homebrewed classes, spells, races etc.
r/DnD – The DnD Reddit page.
r/dndnext – Dnd Reddit page focused on 5e.