No one's mentioned Guniw Tools/Nookicky yet?
A few of my favorite bands:
Guniw Tools: They're a very unusual bunch. The sound varies from rock, to pop, to almost electronic. Sometimes there's even a slight Hindu influence (or at least that's what it sounds like to me). I'd certainly give them a try if nothing else.
(fav songs: Ladybird's Sleeping Art, Plenty of Flour, Baby's One Do)
Nookicky: The lead singer of Guniw Tools's "other" band, this band is a little softer, and poppier in sound I think, but the idea is generally the same.
(fav songs: Rotten, Slipping Star, Itchy Pupy Come)
Shiina Ringo: She's been mentioned before, but I thought I'd reccomend her again. She's got a very unique style, going between a sort of jazzy, to rock, to an orchestrated sound. Very lovely, and often escentric music.
(fav songs: La Salle de Bain, Stoicism, Rinne Highlight)
Buck-Tick: I have to put in a good word for good ol' Sakurai. Buck-Tick generally has a darker feel to it. There's a lot of heavy beats and smooth vocals with rock/electronic overtones.
(fav songs: Muma-The Nightmare, Romance, Gesshoku)
Hmm...personally I don't like Gackt that much >.< I agree with him getting pretty repetitive. lol And I'm sort of holding a grudge since Malice Mizer's break up

but that's just me. lol