Okay, the straight answer for me is the Trampier dungeon master screen. But I didn't use that screen. I made my own out of heavy cardboard, with a strange collage of punk rock art, stuff from Readers Digest and Boys Life, ads for D&D and Time Magazine natural disasters. Half Winston Smith (the punk collage artist), half Max Ernst. And the charts pencilled in on the inside.
Unfortunately that screen was lost to the dust of ages and is no longer available for viewing.
But there's another set of images that I associate with teenage years and the promise of mystery I sought in D&D, though they never appeared in anything by TSR. The illustrations of Sidney Sime.
There was something about those dark, detail-clotted vistas, with tiny human figures skulking and avoiding inky perils - most of the time, without much success. The Lord Dunsany stories they illustrated, when not wonder-tales of imagined orientalist gods, were seedbeds for the larcenous imaginations of Vance and Leiber. The tiny figures were men, good, bad or indifferent, who sought treasure from that which was far beyond them.
At the time, like many teens, I sought mystery, but also its illumination and rationalization - with matrices of encounter tables and saving throws. We have met the Beast and its Hit Dice are 6+6. In a way, to have Sime's illustrations in the D&D books would be to offer a promise the rules could not fulfill - a world more fit for medievalist treasure-seeking using Call of Cthulhu rules, or a set even more deadly and opaque. The clear scenarios of Sutherland and Trampier, horrors front and center, were as Apollonian a monster combat as you could hope for, and even Erol Otus' weird visions made sure to delineate every eyeball and tentacle. A Dunsany terror in D&D rules would be something like "Save each turn vs. death ray or die, otherwise lose 1 level. No stats, can't hit it, can't hurt it."
An out-of-level encounter. A Green Devil Face. No raise, no save, no hope. "It is better not."
See George P. Landow's scans here, in particular the tales of Thangobrind, Nuth and the Gibbelins.
Researcher in social science and appreciator of hexy wargames, role playing games, interactive fiction, board games, and CCGs. I've learned a lot doing design and rules editing work on the side for the Legend of the Five Rings CCG. But this blog is mostly about other things.