You can list songs, artists, albums, genres, storage devices (iTunes vs vinyl), or whatever you like.
I’ll start with listing my top artists in alphabetical order – and I probably omit a lot:
Apocalyptica
Apoptgma Berzerk
Ashbury Heights
Assemblage 23
Code 64
Deine Lakaien
Disturbed
Evanescence
Hammerfall
Icon of Coil
In Extremo
In Flames
Korn
Lasgo
Linkin Park
Metallica
Nightwish
Origa
Solar Fake
VNV Nation