I forgot if I posted here. If I did, then I'm posting again because I can.
In no particular order:
NatsumeRin: Best originality in the community, too bad some of us cannot take in his maps' awesomeness.
Tsuka: Nobody except perhaps the great Mystearica herself maps IIDX songs as well as he does. His use of sliders alone should win him a place in the osu! mappers' Hall of Fame, if such a thing existed.
Mafiamaster: I like to call him the American NatsumeRin (or NatsumeRin the Chinese Mafiamaster, whichever way doesn't make you yell RACIST!), great originality as well as plain fun.
ztrot: Guy has style. You can't challenge this.
val0108: Relatively new Japanese mapper, but looks like he is heading to be one of the greats in the Asian community. Dunno how much water he holds in the overall community, but his maps are full of confidence that is difficult to spot in one's first few maps.
The five I mentioned are, by default, masters of following the music of course. No unnecessary overmapping shit. (*cough*DJPop*cough*)
A few others are also worth mentioning (happy30, GladiOol, Lesjuh, Gabi, Krisom, and MoonFragrance are a few that comes to mind), but those five are my favorite mappers as of right now.