Ballantine published an series of fantasy books between 1969 and 1974. You can read about it on Wikipedia here. In meme fashion, bold those which you have read, they don't have to be in these editions.

These is the precursor series:

1. The Hobbit, J. R. R. Tolkien (Aug. 1965)
2. The Fellowship of the Ring, J. R. R. Tolkien (Oct. 1965)
3. The Two Towers, J. R. R. Tolkien (Oct. 1965)
4. The Return of the King, J. R. R. Tolkien (Dec. 1965)
5. The Tolkien Reader, J. R. R. Tolkien (Sep. 1966)
6. The Worm Ouroboros, E. R. Eddison (Apr. 1967 - later reprinted with colophon)
7. Mistress of Mistresses, E. R. Eddison (Aug. 1967)
8. A Fish Dinner in Memison, E. R. Eddison (Feb. 1968)
9. The Road Goes Ever On, J. R. R. Tolkien and Donald Swann (Oct. 1968)
10. Titus Groan, Mervyn Peake (Oct. 1968 - later reprinted with colophon)
11. Gormenghast, Mervyn Peake (Oct. 1968 - later reprinted with colophon)
12. Titus Alone, Mervyn Peake (Oct. 1968 - later reprinted with colophon)
13. A Voyage to Arcturus, David Lindsay (Nov. 1968 - later reprinted with colophon)
14. The Last Unicorn, Peter S. Beagle (Feb. 1969 - later reprinted with colophon)
15. A Fine and Private Place, Peter S. Beagle (Feb. 1969 - later reprinted with "A Ballantine Adult Fantasy" on the cover)
16. Smith of Wootton Major and Farmer Giles of Ham, J. R. R. Tolkien (Mar. 1969)
17. Tolkien: A Look Behind "The Lord of the Rings", Lin Carter (Mar. 1969)
18. The Mezentian Gate, E. R. Eddison (Apr. 1969)

11/18 for me. And this is the main series:

1. The Blue Star, Fletcher Pratt (May 1969) (#01602)
2. The King of Elfland's Daughter, Lord Dunsany (Jun. 1969) (#01628)
3. The Wood Beyond the World, William Morris (Jul. 1969) (#01652)
4. The Silver Stallion, James Branch Cabell (Aug. 1969) (#01678)
5. Lilith, George MacDonald (Sep. 1969) (#01711)
6. Dragons, Elves, and Heroes, Lin Carter, ed. (Oct. 1969) (#01731)
7. The Young Magicians, Lin Carter, ed. (Oct. 1969) (#01730)
8. Figures of Earth, James Branch Cabell (Nov. 1969) (#01763)
9. The Sorcerer's Ship, Hannes Bok (Dec. 1969) (#01795)
10. Land of Unreason, Fletcher Pratt and L. Sprague de Camp (Jan. 1970) (#01814)
11. The High Place, James Branch Cabell (Feb. 1970) (#01855-9)
12. Lud-in-the-Mist, Hope Mirrlees (Mar. 1970) (#01880-X)
13. At the Edge of the World, Lord Dunsany (Mar. 1970) (#01879-6)
14. Phantastes, George MacDonald (Apr. 1970) (#01902-4)
15. The Dream-Quest of Unknown Kadath, H. P. Lovecraft (May 1970) (#01923-7)
16. Zothique, Clark Ashton Smith (Jun. 1970) (#01938-5)
17. The Shaving of Shagpat, George Meredith (Jul. 1970) (#01958-X)
18. The Island of the Mighty, Evangeline Walton (Jul. 1970) (#01959-8)
19. Deryni Rising, Katherine Kurtz (Aug. 1970) (#01981-4)
20. The Well at the World's End, Vol. 1, William Morris (Aug. 1970) (#01982-2)
21. The Well at the World's End, Vol. 2, William Morris (Sep. 1970) (#02015-4)
22. Golden Cities, Far, Lin Carter, ed. (Oct. 1970) (#02045-6)
23. Beyond the Golden Stair, Hannes Bok (Nov. 1970) (#02093-6)
24. The Broken Sword, Poul Anderson (Jan. 1971) (#02107-X)
25. The Boats of the "Glen Carrig", William Hope Hodgson (Feb. 1971) (#02145-2)
26. The Doom that Came to Sarnath and Other Stories, H. P. Lovecraft (Feb. 1971) (#02146)
27. Something About Eve, James Branch Cabell (Mar. 1971) (#02067-7)
28. Red Moon and Black Mountain, Joy Chant (Mar. 1971) (#02178-9)
29. Hyperborea, Clark Ashton Smith (Apr. 1971) (#02206-8)
30. Don Rodriguez: Chronicles of Shadow Valley, Lord Dunsany (May 1971) (#02244-0)
31. Vathek, William Beckford (Jun. 1971) (#02279-3)
32. The Man Who Was Thursday, G. K. Chesterton (Jul. 1971) (#02305-6)
33. The Children of Llyr, Evangeline Walton (Aug. 1971) (#02332-3)
34. The Cream of the Jest, James Branch Cabell (Sep. 1971) (#02364-1)
35. New Worlds for Old, Lin Carter, ed. (Sep. 1971) (#02365-X)
36. The Spawn of Cthulhu, Lin Carter, ed. (Oct. 1971) (#02394-3)
37. Double Phoenix, Edmund Cooper and Roger Lancelyn Green (Nov. 1971) (#02420-6)
38. The Water of the Wondrous Isles, William Morris (Nov. 1971) (#02421-4)
39. Khaled, F. Marion Crawford (Dec. 1971) (#02446-X)
40. The World's Desire, H. Rider Haggard and Andrew Lang (Jan. 1972) (#02467-2)
41. Xiccarph, Clark Ashton Smith (Feb. 1972) (#02501-6)
42. The Lost Continent, C. J. Cutcliffe Hyne (Feb. 1972) (#02502-4)
43. Discoveries in Fantasy, Lin Carter, ed. (Mar. 1972) (#02546-6)
44. Domnei, James Branch Cabell (Mar. 1972) (#02545-8)
45. Kai Lung's Golden Hours, Ernest Bramah (Apr. 1972) (#02574-1)
46. Deryni Checkmate, Katherine Kurtz (May 1972) (#02598-9)
47. Beyond the Fields We Know, Lord Dunsany (May 1972) (#02599-7)
48. The Three Impostors, Arthur Machen (Jun. 1972) (#02643-8)
49. The Night Land, Vol. 1, William Hope Hodgson (Jul. 1972) (#02669-1)
50. The Night Land, Vol. 2, William Hope Hodgson (Jul. 1972) (#02670-5)
51. The Song of Rhiannon, Evangeline Walton (Aug. 1972) (#02773-6)
52. Great Short Novels of Adult Fantasy I, Lin Carter, ed. (Sep. 1972) (#02789-2)
53. Evenor, George MacDonald (Nov. 1972) (#02874)
54. Orlando Furioso: The Ring of Angelica, Volume 1, Ludovico Ariosto, translated by Richard Hodgens (Jan. 1973) (#03057-5)
55. The Charwoman's Shadow, Lord Dunsany (Feb. 1973) (#03085-0)
56. Great Short Novels of Adult Fantasy Volume II, Lin Carter, ed. (Mar. 1973) (#03162-8)
57. The Sundering Flood, William Morris (May 1973) (#03261-6)
58. Imaginary Worlds: the Art of Fantasy, Lin Carter (Jun. 1973) (#03309-4)
59. Poseidonis, Clark Ashton Smith (Jul. 1973) (#03353-1)
60. Excalibur, Sanders Anne Laubenthal (Aug. 1973) (#23416-2)
61. High Deryni, Katherine Kurtz (Sep. 1973) (#23485-5)
62. Hrolf Kraki's Saga, Poul Anderson (Oct. 1973) (#23562-2)
63. The People of the Mist, H. Rider Haggard (Dec. 1973) (#23660-2)
64. Kai Lung Unrolls His Mat, Ernest Bramah (Feb. 1974) (#023787-0)
65. Over the Hills and Far Away, Lord Dunsany (Apr. 1974) (#023886-9)

I've done 17/65 out of these