Music of the Ainur is a music pack that adds a variety of classical-ish music to Middle-earth. With famous works such as the symphonies of Beethoven to folk songs of the Middle-east, Music of the Ainur contains over 100 unique works. It's my hope that this adds a new element to your exploration of Middle-earth.
It is highly recommended that you increase the minimum time between tracks (you can do this by clicking 'mods' from Minecraft's main menu), or that you use it in conjunction with another music pack.
Due to the way the music system works, sometimes tracks will continue to play even if you've left the area they are meant to play in. If this bothers you too much, you can reset the music by going into your options, turning music off, returning to the game, and then going back to options to turn music back on.
If you're interested, I have another music pack, Ambience of Middle-earth, that you can find here.
Music of the Ainur can be downloaded here. The current version is Alpha 1.
If you have any issues with the music pack, such as poor quality tracks or things that don't seem to fit in the biome they play in, you can report them here, as can any suggestions for new tracks.