The Lord of the Rings, by J.R.R. Tolkien, is all one book really, but
it's most often found published in three volumes:
The Fellowship of the Ring, The Two Towers, and The Return of the King.
Each of these volumes has what Tolkien termed "Books"; for example, The Fellowship of the Ring consists of Book I and Book II of The Lord of the Rings.
Without a doubt these are the best of Tolkien's existing works on Middle-earth, and the only undisputedly canonical source. Those readers who disliked the light or childish tone of The Hobbit may not like the first six to eight chapters; I usually recommend that people read all of Book One (the first half of The Fellowship of the Ring) before giving up. If they aren't interested yet, then I'll admit that Tolkien probably isn't right for them.
The Reader's Maps to the Lord of the Rings are provided to orient you while you are reading the book. Tolkien constantly refers to the places of Middle Earth in the story, and it's very easy to become overwhelmed with all the strange place-names. To access the maps, click on the titles listed above.
About Making Maps of Middle-earth
When The Hobbit was published in 1937, it contained maps drawn by Tolkien, showing a small part of Middle-earth (the north-west corner of the map); but when, soon afterwards, he began work on a sequel, he extended the geography of Middle-earth and, assisted by his son, Christopher, made many more maps. As the story developed these maps were constantly being re-drawn. Names were changed and roads and rivers diverted. 'If you're going to have a complicated story', he once explained, 'you must work to a map; otherwise you'll never make a map of it afterwards.'
It took twelve years for the story of Bilbo's nephew Frodo and his quest to destroy Sauron's Ring to grow in The Lord of the Rings, and when it was finally published in three volumes in 1954 (Parts I and II) and 1955 (Part III), the books contained a map of Middle-earth made by Christopher Tolkien.