Random House’s Suvudu blog has a cool post on metal songs based on fantasy novels. Of course, I had to chime in with some additions in the comments, which I’ll duplicate here:

• Amon Amarth–who are obviously named after Mount Doom, though they generally sing about Vikings–have a song called “Amon Amarth,” in which they reference Mount Doom, but they also mention Vikings, so I don’t know if it counts as being “based on” Tolkien.
• Every song by Battlelore. I knew that they sang about swords-and-sorcery sort of topics, but wasn’t sure until I checked Wikipedia just now–apparently ALL of their lyrics are derived from Tolkien. Which is appropriate, because I always pictured the dueling vocalists as an orc and an elf singing. (Give them a listen and you’ll know why.)
• A band called Jester’s Funeral adapted a bunch of John Shirley stories into songs for one of their albums (which they released online for free), called Fragments of an Exploded Heart.
• If Dante’s The Divine Comedy counts as fantasy, then this counts for the list: Sepultura did an album based on that.
• White Zombie’s “I am Legend” is based on I am Legend.
   

Can you think of any others not mentioned by me, or the original list?