The Mad Capsule Markets are the best band on earth - get Osc-Dis as its well amazing, plus Takeshi Ueda is the god of bass...

If you're downloading I recommend Midi Surf, Island, Tribe, Bit Crusherrr, Come, Chaos Step, Gaga Life, Scary, Systematic.....*carries on mumbling other amazing songs by them*

I kind of like one or two songs by Ayumi Hamasaki but I don't know much about J-Pop.