If Someone Was To Ask You What Books You Think Of As Special Books What Would You Say?

Important reference books to have include more than one dictionary. I have a Webster's from about 40 years ago that has very different entries than a modern Webster's. I also have a third modern dictionary, all for cross-reference purposes.
A good thesaurus is a must, as is an atlas.
If you are a serious writer, the standard text in the U.S. for usage is the Chicago Manual of Style. If you are a journalist, you must essentially memorize the Associated Press Style book. I also have a very handy "dictionary of troublesome words."
You may also want dictionaries of foreign languages; in the western U.S., a Spanish dictionary is a must.
I keep a complete Shakespeare, both volumes of the Norton Anthology of English Literature, and Bullfinch's Mythology nearby as reference books.
Yes, you can now find all of this info online, but, personally, it's quicker to just look it up in a real book.

I have a degree in English literature. I have kept a list of every single fiction book I have read since 1970. I rate the best with symbol indicating "very good" and "excellent." Here are some that achieved the highest rating:
"The Moon is Down" and "East of Eden" -- John Steinbeck
"The Chosen" -- Bernard Malamud
"Lord of the flies" -- William Golding
Anything by Oscar Wilde
"A Death in the Family" -- William Agee
"Moby Dick" -- Herman Melville
"The Idiot" -- Fyodor Dostoyevsky
anything by William Faulkner, especially "Absalom, Absalom!" and "Light in August"
anything by Thomas Mann, especially "Magic Mountain" and "Death in Venice"
anything by Henry James, especially "The Golden Bowl" and "Portrait of a Lady"
"Passage to India" -- E.M. Forster
"Anna Karenina" -- Leo Tolstoy
any play by Henrik Ibsen
anything by James Joyce, especially "Ulysses" and "Portrait of the Artist as a Young Man"
anything by William Styron, especially "Sophie's Choice"
anything by Thomas Hardy, especially "Jude the Obscure"
anything by Jane Smiley, especially "One Thousand Acres" and "Prodigal Summer"
anything by Tony Hillerman
anything by John Irving
anything by Cormac McCarthy, especially "All the Pretty Horses"
"Les Miserables" -- Victor Hugo
That oughta get you started!!

Well as a book lover this is the perfect question, as I devour books. I sometimes have to be careful if I have a deadline looming for writing, because once I start a good book I will read through the night and be shattered the next day.
I list here some of my favourites.
Out of Africa, Isak Dinesen
The English Patient, Michael Ondantjie
Tess of D' Urbavilles Thomas Hardy.
All of D.H. Lawrence's books, England my England,Sons and lovers, and especially his writings on Italy.
E.M. Forster's book "Where angels fear to tread".
J. M. Coetzee's works on Africa and,
Alexandra Fuller's book on her African childhood, "Don't lets go to the dogs tonight" , it's sheer brillance rates with Peter Godwin's "Makiwa".Both are blindingly funny, sad and real.
Alan Paton's, "Cry the beloved country".
George Orwell's animal farm.
Tim Parks in Italian neighbours.
There are lists of books and I could go on, but I have listed some that I come back to regularly