The fact is that I wouldn't change the list much, other than to add a couple of novels such as Lanier's second Hiero yarn, Piers Anthony's Split Infinity series, and the Disc World books.I find this a very interesting answer for several reasons. Firstly, I think it significant that Gary, late in his life, still felt that the selections in Appendix N, which was made up primarily of books written before 1970, was representative of D&D's inspirations. This jibes well with my own intuition that D&D, particularly in its Gygaxian form, is something of a nostalgia project. By that I mean only that many of the fantasy/science fiction sources from which it drew were "old fashioned" even in 1974. Those sources had wider currency then, because of the pulp reprint explosion of the late 60s and early 70s. Likewise, those reprints inspired many then-contemporary writers to pen their own tales in the same vein, which further fed the somewhat "antique" approach to fantasy that Gygax favored and promoted. I personally connect D&D very strongly with these "archaic" approaches to fantasy, which feel to me far more alien and fantastic than modern, post-D&D fantasy.
I would never add other media forms to a reading list. If someone is interested in comic books and.or graphic novels, they're on their own.
Secondly, it's noteworthy that Gary didn't mention Glen Cook's Black Company series, one of the few bits of post-70s fantasy writing I recall his ever endorsing as being in the same spirit of D&D. He may simply have forgotten them, but, if so, that too is perhaps telling. Thirdly, the reference to Discworld might, on first glance, seem an oddity, but remember that Gary was an accomplished punster. He no doubt took great pleasure in Terry Pratchett's similar facility in that form of humor, which I have long argued is an important part of the Gygaxian feel.
Lots of food for thought in just a few words. Thanks, Allan!