Metal based on literature

Blind Guardian - Nightfall in Middle Earth (whole album)
Blind Guardian - And Then There Was Silence
Iced Earth - The entire album of Burnt Offerings. A theme album about Hell.
Iced Earth - The Something Wicked Trilogy
Iced Earth - The Entire Album of Horror Show. A theme album about Folk Lore Monsters.
Iron Maiden - Brave New World
Iron Maiden - Flight of Icarus (as said previously)
Iron Maiden - Rime of the Ancient Mariner
Iron Maiden - The Number of the Beast
Kamelot - Epica (whole album)
Kamelot - The Black Halo (whole album)
Kamelot - The Shadow of Uther
Symphony X - Through the Looking Glass
Symphony X - The Odyssey :notworthy
Symphony X - V: The New Mythology Suite (whole album)

Those are all only off the top of my head.
 
Drudkh uses some lyrics from the poet Taras Shevchenko, and I enjoy them.

Summoning notes their primary influence as Tolkien also, and a lot of their lyrics relate to Middle-Earth, and I enjoy them.
 
Tons of power metal is. I'm not a big power metal fan, but I like Grave Digger, and many of their albums are based on literature (Rheingold is based on The Niebelungenlied, Excalibur is based on the King Arthur story, and Tunes of War is based on some Scottish tale). Orphaned Land's most recent work is based on the Noah's Ark story of the Bible/Torah.;) Many of the songs on Amorphis' Tales from the Thousand Lakes are based on Finnish myths.
 
Morbid Angel-Angel of Disease and The Ancient Ones, both based on Lovecraft's Simon Necronomicon. Trey's stage last name Azagthoth comes from the Simon Necromonicon as well.