Jack Vance's Dying Earth books: the DnD magic system (aka: Vancian Magic) is basically cut whole cloth from these books. Likewise the "iconic" picture of a high-level archmage is taken from here as are many specific magic items (IOUN stones) and spells (Excellent Prismatic Spray).
Michael Moorcock's Eternal Champion books (espically the Elric books): inspired the alignment system as a way of choosing sides in a cosmic war, inspired the cosmology of many planes (and the plane-hopping adventure) and the idea of very personal gods who reside there and make war on each other via their mortal servants/proxies. Also inspired some specific magic items espically inteligent magic items. Also I think you could say Elric inspired the entire line of summoning spells as I don't think any of the other literary sources focused on calling extra-planar allies so much.
REH's Conan: influenced the mechanics less than it did the general flavor of mercenary adventure; every time you break into a wizard's tower, raid the ancient tomb beneath a parymaid or end an adventure by declaring that you are blowing your share of the loot on "ale and whores" you are paying homage to Conan.
I am not so familiar with many of the other "inspirations" as I should be

Time to start hitting up the old used book store again!
Oh, and to be perfectly honest. I personally do
not believe that Tolkien is as much of an influence on DnD as many people like to believe he is. Looking at the foundations of DnD I see that the good Professor gave us: the racial archtypes (Dwarves, Elves, Hobbits, Orcs), the concept that the adventuring party should be a "felowship" of different races and professional skill-sets, the classical "fallen Dwarven kingdom under the mountain" adventure, the classical "raid the Dragon's horde under the mountain" adventure, a few specific magic items and a few specific monsters and character archtypes (wizards in pointy hats). Regardless of the fact that many specific individual DM's pattern their campaigins after the quest of the Ring I still say that if you simply read through the PHB and DMG that, even today, the influence of the other authors mentioned in this thread is much greater than that of JRRT.
Later.