I think everyone's music preferences would be:
Aragorn: He listens to that pump up music like Rocky's theme and Eye of the Tiger, Man in Motion. "I'm the man" music. Secretly listens to Vanilla Ice during his workout.
Gandalf: ProgRock....brainy, grand, majestic music. He has a closet KISS fetish because once he went to a concert and loved the pyrotechnics on stage.
Elves: New age, Bach, Mozart, their music would need to be complicated and beautiful, harmonious.
Dwarves: they like metal or industrial with a pop twist....Nails? When they get on a soapbox (which is often, for they are a proud people and also very short and selfconscious about it) they pull out the Marilyn Manson. "THE BEAUTIFUL PEOPLE..uh-ahhh!"
Hobbits: They probably like country music or Irish folk music, also 59th St Bridge Song (feelin groovy). They headbang at Irish Rover concerts. They particularly enjoyed it when "Don't Worry Be Happy" came out, but when Belladonna Took (the adventurous one) bought Bobby McFerrin's next CD she found it just wasn't the same and gave it to Gandalf to place under the next round of fireworks.
Rohan: Mr. Ed theme song....hahaha. Cowboy songs like Sweet Baby James or Marty Robbins tunes.
The Roharrim: They like the Doors songs where Jim doesn't scream, it spooks the horses when that happens. Their theme song is "Riders on the Storm".
Gondor: Pop country like Garth Brooks and 80's pop metal. They also might like the Blues. Blue collar music, they work HARD. The rebels in Gondor like Metallica.
Boromir: I think this guy likes Bob Seger...he may be honorable but he likes the part about "points all her own sittin way up high." Also has been known to get ready for battle by listening to college fight songs. Liked Milli Vanilli at first (never told anyone about it) but when he found out that they had to give back their Grammy he secretly burned THAT cassette, because Boromir does not like liars.
Ents: ENYA in memory of Trees. And since they lost their "wimmen" they might like the blues and some of the old country songs about heartbreak.
Tom Bombadil: writes his own songs and sing em!
Sam: Folk music...hippy songs. Maybe Billy Joel and Elton John, John Denver. He's not as dumpy as he may appear.
Sauron: dark dark metal or stravinskyish classical. Listens to Yanni, but only before bed and no one else knows. May have liked beatnik jazz before he became a bad guy.
Elrond: This guy rocks out to Wagner and meditation music. When he's feeling nostalgic he gets out his old Motown records.
Frodo: he digs stuff like Hootie and the Blowfish and Dave Matthews, Sarah McLachlan. Pop, easily accessible but a little smarter, after all, he knows his letters!
Bree: these folks are a mixed bag of men and hobbits, coexisting in harmony. I would say they enjoy John Lennon and protest songs. When they party up, they like both Sly and the Family Stone AND the Rolling Stones.
Bilbo: Also writes his own songs and he is frontman for an elf music tribute band. REALLY likes that extremely long song about the shipwreck that Gordon Lightfoot did.
Arwen: DUH?? AEROSMITH! hahaha. she LOOVES her daddy. Can you picture Elrond doin the Steven Tyler strut and twirling his mike stand around with a scarf tied to it? Yet, he doesn't have Stevie's lips.
Gollum: He thinks Michael Jackson is just (can I say it?) precious! He can definitely relate to all those changes in MJ's appearance. Didn't like the song Man in the Mirror though.
Galadriel: Joni Mitchell and Judy Collins, Carole King, definitely the female powerhouse songwriters... also Annie Lennox, and Aretha Franklin...R-E-S-P-E-C-T
Legolas: YEP Dan Fogelburg it is, James Taylor, Simon and Garfunkel and Jim Croce too. All that sensitive storytelling stuff from the 70s. Also known to listen to U2 and RATM when he is particularly fired up. Went through a George Michael phase but it didn't last very long.
Merry and Pippen: TV theme songs. "Just sit right back and you'll hear a tale, a tale of a fateful ship." as well as a great number of cartoon themes. "If nautical mayhem be something you wish (SPONGE! BOB! SQUARE! PANTS!) then hop on the deck and flop like a fish!" Jane's Addiction "Been Caught Stealing". After their coming of age, they discovered Weird Al.
The Black Riders: these guys are tough. They are former Kings after all, their music would not be stuff that commoners enjoy. And yet they are evil.....so let's just make them listen to Whitney Houston, Will Smith, and Celine Dion, even if only because we know they will hate it.
Several people mentioned the orcs. Um. It could be argued that they don't listen to music at all because their hearts are so FULL OF HATE that there is NO ROOM for beauty no matter how you define it and all music has a quality of beauty to it... If they listen to anything it's got to be death metal or gansta rap, the really mean stuff. During mating, they bring it down a few notches. I agree that Barry White is appropriate, also Prince and Madonna, and that new Nelly song "It's gettin hot in here, so take off all your clothes...!" After a particularly detrimental battle where they have lost a lot of troops, such as their little run in with the Riders of Rohan, they may make up for their losses with a little Marvin Gaye...."wooooooo! Let's get it ON"