Mix of Jpop, Jrock, Visual Kei, Euro/Guro names (some of them just go all over the board) that I enjoy:
Maaya Sakamoto-- familiar with Escaflowne or RahXephon? The opening themes are hers, along with the image songs. Some of her stuff is rather filk in style
Gackt-- dresses up like Char from Z Gundam currently. Getting back into his older style and losing all the random "wooo-ooo-oooo" warbling and overused dakishimetes is good for him. I don't think he's made anything I don't like though
L'Arc~en~Ciel (also P'unk~en~Ciel and D'ark~en~Ciel)-- watch FMA? READY STEADY GO is their work. Also featured in Kenshin (The Fourth Avenue Cafe) and who knows how many other animes
Dir en Grey -- scary fangirls, good music. Harder stuff with occassional Kyo scream, but they do the occassional ballad too (including full orchestra in Ain't Afraid to Die~with frosted ambience)
Miyavi-- varies with the song. If you like Dir en Grey, you might enjoy it.
SID-- somewhat jazzy. Mao sings with a odd sort of breathy desperation.
Malice Mizer -- their style depends somewhat on which "era" the song was made during (Tetsu, Gackt, Klaha). the Gackt stuff is somewhat more catchy (e.g. Brise, Ma Cherie, Apres Midi); the Klaha era is a bit harder
Hide (of X-Japan)-- if for nothing more than his awesome guitar ability
Hyde (of L'Arc~en~Ciel)-- if you like his band, you'll probably like his solo work
Asian Kung-Fu Generation -- of Naruto and FMA fame. catchy stuff
Orange Range -- of Bleach fame. They make me think of a mix of Porno Graffiti and Asian Kung-Fu Generation
Porno Graffiti-- the song Melissa and Agehachou is a good place to start. fast paced, bouncy, depressing lyrics to happy music much?
Yoko Kanno-- Did you like the music from Cowbow Bebop or Wolf's Rain? you already like her work
I don't know why, but a lot of Two Mix's music makes me think of Take on Me. Best way I know to describe them. I also think very much of the 80's.
And does anyone remember Luna Sea?
Anyway I'm done recommending for now ^^