Plus-Tech Squeezebox: I am an unashamed fan of Shibuya-kei. If you've never heard of it, it's kind of a mix of Bossa Nova, J-pop, Hip-hop and Electropop. You may notice that that sounds like a bad idea, but it really works in practice. Trust me. Plus-Tech Squeezebox are further on the electropop side than many other artists, but I think it works in their favor. Goddamned catchy songs.
Yukari Fresh: Another shibuya-kei artist, she leans more on hiphop elements (sampling, warm thick drums) and still makes some really catchy pop songs.
Ground Zero: In this case I'm referring to the Otomo Yoshihide jazz/noise rock/metal group. Seriously insane music. Mixes a lot of different influences into something really unique. Otomo Yoshihide's New Jazz Orchestra is kind of the same thing.
There's also Limited Express (has gone?), Shonen Knife, Satoko Fujii, The 5.6.7.8's, Takako Minekawa, The Flying Luttenbachers, Trs-80, Hazel Nuts Chocolate, Macdonald Duck Eclair, Fennesz, Boris, 2562, Ikue Mori, Hella, Shellac, Kiiiiiii, Chieko Mori, Michiyo Yagi, Oval, Puzzleweasel, Soundmurderer and MIDORI (the punk band, not the other ones).
I want to write a little about all of them (and the ones I posted earlier) but it is
damned late over here and I've already posted too much in this thread.