1. I really like The Guide to Middle-earth. Whenever I need to lookup a name, location, thing, battle, etc. it is there.
2.
Let's see...
The Hobbit
Lord of the Rings: The Fellowship of the Ring
Lord of the Rings: The Two Towers
Lord of the Rings: The Return of the King
The Simarillion
Unfinished Tales
The Book of Lost Tales (History of Middle-earth, volume 1)
The Book of Lost Tales 2 (History of Middle-earth, volume 2)
The Lays of Beleriand (History of Middle-earth, volume 3)
The Shaping of Middle-earth (History of Middle-earth, volume 4)
The Lost Road and other Writings (History of Middle-earth, volume 5)
The Return of the Shadow (History of Middle-earth, volume 6 [History of The Lord of the Rings, part 1])
The Treason of Isengard (History of Middle-earth, volume 7 [History of The Lord of the Rings, part 2])
The War of the Ring (History of Middle-earth, volume 8 [History of The Lord of the Rings, part 3])
Sauron Defeated: The End of the Third Age (History of Middle-earth, volume 9)
Morgoth's Ring: The Later Simarillion, Part 1 (History of Middle-earth, volume 10)
The War of the Jewels: The Later Simarillion, Part 2 (History of Middle-earth, volume 11)
The Peoples of Middle-earth (History of Middle-earth, volume 12)
Another extremely valuable book to have is The Letters of JRR Tolkien. To me anyway 😛
🙂