Tolkien's epic The Lord of the Rings is essential reading for those interested in Middle-earth. The novel contains three volumes: The Fellowship of the Ring (1954), The Two Towers (1955), and The Return of the King (1955). It chronicles the adventures of Frodo, Bilbo's nephew, and his quest to destroy the ring of power discovered in The Hobbit.
The Silmarillion (1977) was published after Tolkien's death. His son, Christopher, compiled the book from various fragments written before The Hobbit and The Lord of the Rings. It details the ancient history of Middle-earth.
C. S. Lewis wrote a seven-volume children's fantasy series called The Chronicles of Narnia. The series follows the adventures of four children who discover a magical world of talking animals, witches, and dwarves behind a wardrobe in an old house. The first book published in the series, The Lion, the Witch, and the Wardrobe (1950), is a good place to start.
Daniel Grotta's J. R. R. Tolkien: Architect of Middle-earth (1976) is a compelling account of Tolkien's life and works. Grotta discusses the influences on Tolkien's fiction and provides an in-depth analysis of his major works.
Fritz Leiber wrote dozens of stories featuring his Fafhrd, a barbarian, and the Gray Mouser, a cynical thief. Their adventures in the world of New-hon are exciting and original. Ill Met in Lankhmar (1995) contains the first two collections of his Fafhrd and Gray Mouser stories. It is a good introduction to the fascinating realm of Newhon.
Author Michael Moorcock's Elric series is captivating for those readers interested in fantasy literature. The protagonist, Elric, is an evil elf whose sword, Stormbringer, steals souls. Elric of Melnibone (1972) is the first novel in the series.