The Librarything site (of which I am a member) has a section for the books read and/or kept in personal libraries by famous writers, and C. S. Lewis’s is here.
There’s 44 pages to it, each page hosting 50 books… so yeah, there’s a lot, especially of history, natural history, religion, and philosophy. But taking a look at the books classed as fantasy, of which there are 85, I see fantasy pioneers James Branch Cabell, L. Frank Baum (creator of Oz), pulp writer H. Rider Haggard, George MacDonald, Charles Kingsley (The Water Babies), Lord Dunsany, Edith Nesbit, and William Morris. All of these authors have been mentioned by Lewis scholars.
I was also right about Lewis being a fan of the Lovecraft Mythos, as was hinted at in The Silver Chair; one of the books was by Robert Bloch, Lovecraft’s longtime collaborator.
For Lewis’s post-1920s books, there were a few surprises, like Jane Gaskell, Isak Dineson, Virginia Wolff (author of the gender-bending Orlando — whose titular character was portrayed in a movie by Tilda Swinton, the later White Witch!) and James Thurber.
Other tidbits:
Courtesy of the Narniaweb site: C. S. Lewis wrote two poems inspired by Narnia, known collectively as the Narnian Suite, a marching song for Dwarves and a contrasting one for Giants.
Brent Dickieson’s wonderful site A Pigrim in Narnia site has this informative post on where and how to find more obscure articles about C. S. Lewis, J. R. R. Tolkien, and the other Inklings.
Through the above, I found this paper on Disney’s film adaptation of Prince Caspian.
And also movie-related, this podcast on the failures of Disney’s The Voyage of the Dawn Treader movie.