The introduction discusses a bit of how Gary came to his list here and also suggests several more sources for inspirational reading. This is the introduction:
Inspiration for all the fantasy work I have done stems directly from the love my father showed when I was a tad, for he spent many hours telling me stories he made up as he went along, tales of cloaked old men who could grant wishes, of magic rings and enchanted swords, or wicked sorcerors [sic] and dauntless swordsmen.
Then too, countless hundreds of comic books went down, and the long-gone EC ones certainly had their effect. Science fiction, fantasy, and horror movies were a big influence. In fact, all of us tend to get ample helpings of fantasy when we are very young from fairy tales such as those written by the Brothers Grimm and Andrew Lang. This often leads to reading books of mythology, paging through bestiaries, and consultation of compilations of the myths of various lands and peoples.
Upon such a base I built my interest in fantasy, being an avid reader of all science fiction and fantasy literature since 1950. The following authors were of particular inspiration to me. In some cases I cite specific works, in others, I simply recommend all of their fantasy writing to you. From such sources, as well as any other imaginative writing or screenplay, you will be able to pluck kernels from which will grow the fruits of exciting campaigns. Good reading!
In the first paragraph, we see a nod toward accumulating fantasy stories and folktales generally. Gary gives homage to his father for simply telling fantastic tales when Gary was a child. This kind of childhood storytelling no doubt influenced most of us to be interested in fantasy. It doesn't recommend any particular stories, but rather the idea of storytelling and shared fantasy in general.
Next, we get suggestions of possible sources outside of traditional fiction. Comics and movies can definitely be sources of inspiration for gaming. I am not including them in the list at present, but I may come back to add them later. Fairy tales can also be a great inspiration, and here Gary gives us some specific suggestions. The Grimm fairy tales are available in a lot of different editions. I am going to add them under the title of the common collection, rather than specifying a particular edition. Andrew Lang published twelve collections of fairy stories titled by the color of the books. These are also going on the list.
The reference to mythology and beastiaries opens the possibility of a huge amount of reading. Virtually any mythology can be incorporated into a game setting if you work at it. That means we could conceivably add all kinds of things to the list to account for mythology. Rather than bury everything else in a bibliography of mythology texts, I am adding the one that most of us used to discover mythology in the first place, Bulfinch's Mythology. I'll add more mythology later.
The final paragraph of the introduction states that the authors and works listed were the ones that particularly influenced Gary, not that they are an exhaustive list. I think this points to something important to remember in terms of using these sources. Anything can give a good idea for a bit for a game, some works or authors will be particularly relevant or influential, but you need to pick and choose what you use. Unless you're running a game completely within a particular fictional setting, harvest your reading and viewing for ideas that you can combine to make something new.
Next I'll start looking at the individual authors on the list in the appendix.