The most important source for Vancian magic, "Mazirian the Magician", feels D&D-y in a way that almost all other fantasy fiction doesn't: not only does the protagonist encounter many different monsters and other dangers, these are gathered together in a small geographic area. D&D and "Mazirian the Magician" are monster dense.
This post describes the resemblances between Jack Vance's short story "Mazirian the Magician" and D&D in more detail. It was published in 1950 as part of
The Dying Earth. The spell memorisation and casting is very similar to D&D. But it's also a story about resource management, and those resources getting used up by a large number of encounters with monsters and other dangers.
"Mazirian the Magician", like D&D, distinguishes between spells known and spells memorised. The former are much greater than the latter:
Only a few more than a hundred spells remained to the knowledge of man. Of these, Mazirian had access to seventy-three.
Mazirian, by dint of stringent exercise, could encompass four of the most formidable, or six of the lesser spells.
Mazirian made a selection from his books and with great effort forced five spells upon his brain: Phandaal's Gyrator, Felojun's Second Hypnotic Spell, The Excellent Prismatic Spray, The Charm of Untiring Nourishment, and the Spell of the Omnipotent Sphere.
The story mostly consists of a pursuit thru a very dangerous wilderness. Mazirian is chasing T'sain, with the aim of imprisoning and enslaving her.
Mazirian's spell use is as follows:
He uses Phandaal's Gyrator to kill a deodand. "Thrang the ghoul-bear" is slain by the Excellent Prismatic Spray. Mazirian casts the Charm of Untiring Nourishment to follow T'sain underwater. When he is trapped beneath stone blocks he frees himself with the Spell of the Omnipotent Sphere. He uses his last magic, Felojun's Second Hypnotic Spell, to deal with "vampire-weed". Now out of spells he is killed when he encounters animate trees that use their branches like whips, and T'sain is able to escape.
Resource management is explicitly a concern: "Mazirian paused indecisively. It was not good to use so many spells and thus shear himself of power."
Mazirian's Live Boots, similar to Boots of Speed or Boots of Striding and Springing in D&D, are also a limited resource: "The spring and drive began to leave the Live Boots, for they had come far and at great speed." "Mazirian made one effort to follow, and discovered that his Boots hung lax and flaccid—dead."
It can be seen from the examples above that this story, like D&D, features a lot of monsters and a lot of magic. Outside, there are also Twk-men, who are tiny and ride dragonflies, and pelgranes, dangerous flying beasts. Mazirian's mansion contains a carnivorous plant, a miniature dragon – which Mazirian uses to threaten Turjan, a wizard he has imprisoned and miniaturised – and an artificial man, like a homunculus. T'sain is also an artificial being, created by Turjan in a previous story. T'sain had two spells memorised – "the Charm of Untiring Nourishment and a spell affording strength to her arms" – and also possessed an anti-magic rune that protected her from Mazirian's spells.
The only other comparably 'monster dense' story from the same period I know is Manly Wade Wellman's "The Desrick on Yandro" in
The Magazine of Fantasy and Science Fiction (June 1952). This has many brilliantly weird monsters – the Toller, the Flat, the Bammat, the Behinder, the Skim, and the Culverin. However they are all part of a single encounter.