J-Pop is really expensive to import. I have heard of Gackt, but not any of the others. What I usually do is find a song from a particular artist, and if I like it, I will go the extra mile and buy the CDs from Japan. My Ayu collection isn't even close to being finished: I only have Rainbow, Guilty, and Secret (which is coming in the mail very soon), along with a bunch of singles that I didn't technically buy -.-.
I normally try to avoid singles because they are too pricey for the amount of stuff on them, but now that I'm looking at Mirrorcle World, it looks really cool, considering Mirror was awesome.
So, right now, I'm focusing on her main albums, because that's where the goods are.
But, I do have Porno Graffitti's THUMPx and Siam Shade's III and IV. I like Ayumi Hamasaki the best, however. I've certainly been listening to Guilty almost constantly. I don't think there's a single song on there that I dislike, which is extremely rare for any album I hear. For some reason, glitter is the catchiest one on there, so I like just putting on the Repeat and listen to that one over and over.
For multiple days straight.