I have a 30g Creative Zen W. It is full, and my computer has probably 60g of just music on it. I also have like 400 cds, 100 or so on vinyl. And then there's my Rhapsody subscription. So yeah, waaay too much to list, but here is some of what I have:
Complete works of Led Zeppelin (my favorite classic rock band), Andrew Bird (I love him. A lot.), Muse, Sufjan Stevens, Belle & Sebastian, The Decemberists, The Beatles, Elliott Smith, The White Stripes, Regina Spektor, and Spoon.
Also got scattered albums of AC/DC, CCR, Cat Stevens, AFI, The Killers, Death Cab For Cutie, a crapload of Hendrix and David Bowie, Modest Mouse, Fleet Foxes, Frightened Rabbit, Django Reinhardt & Steppane Grappelli, Dosh, The Magic Numbers, Arlo Guthrie, Pink Floyd, The Doors, Ween, Islands, Keane, New Pornographers, The Dears, The National, The Zombies, Beirut, The Who, Yes, Rufus Wainwright, The Stills, Elbow, Simon & Garfunkel, Jack Johnson, Cream, Yann Tiersen, Flogging Molly, Gogol Bordello, She & Him, Feist, Spike Jones, Duke Ellington, Hans Zimmer, Queen, Murder By Death, Snow Patrol, The Chieftains, James Newton Howard, The Arcade Fire... and a lot more.
If it has a rock, folk, jazz, or classical element, I'll listen to it. I think that's why I love Andrew Bird so much, he combines it all, and then some.