Ready for a big list?
A: Ayumi Hamasaki (duh)/ABBA/Adam Nickey/Above & Beyond/Alabaster/Ai Otsuka/alan/Ami Suzuki/Armin van Buuren/Ashlee Simpson
B: BoA/Betwixt & Between
C: capsule/Cold Blue/chum
D: Dan Stone/Daniel Kandi/DJ Amaya
E: Eiko Shimamiya/Every Little Thing/eufonius
F: Freezepop
G: GIRL NEXT DOOR/globe
H: Hilary Duff
I: Igor Sapunov
J: Jono Grant
K: KOTOKO/Koda Kumi/Kaori Utatsuki/KOJA YUKINO
L: Lia/Lady Gaga
M: m.o.v.e/Mat Zo/Maor Levi/Mami Kawada/MELL/Miley Cyrus/Miyuki Hashimoto
N: Nami Tamaki/Namie Amuro/Nitrous Oxide
O: OceanLab/Oliver Smith/The Orb/Origa
P: Perfume
Q: -no artist-
R: REDALiCE/Rita/Riyu Kosaka
S: Son Dam Bi/Sunny Lax/Super8 & Tab
T: teranoid/Temple One/T.M. Revolution/Thanatos/TWO-MIX
U: Utada Hikaru
V: -insert all Vocaloids here-
W: Wellenrausch
X: -no artist-
Y: YUI/YURIA/Yui Sakakibara/YOSHIMUNE SAUNDOTORAKKU
Z: -no artist-
...wow, I can't believe I typed that all out! As you can see I have a varied music taste, mostly Trance and Japanese Pop.