The OD&D supplement I wanted the longest is now out on DriveThruRPG.
Supplement III: Eldritch Wizardry.
This was the one that grabbed my attention the most back in the day.
Though this is the cover that I know best.
Demons, Artifacts, Psychic Powers, Druids. Everything I wanted in MY D&D. It was also missing the one thing I felt it needed above all else. Witches.
It is also the spiritual godfather to many of my witch books, especially "Eldritch Witchery".
Why not pick them both up today!!