Sekken-ya; a Japanese rock group that does covers of a lot of music from the Touhou series of games, in particular I'd recommend the songs D-89 and 二足歩行の天狗walkin'.
403 Forbiddena; Japanese power metal. They don't seem to have quite as large of a discography, but are still very good. Northern Lights, Southern Cross and Blaze of Life are all good. As a note though, they sing in English, it's just kinda broken sometimes.
Turbo; Korean dance group, kinda reminiscent of 90's boybands, but good anyways.
http://www.youtube.com/watch?v=6M3Paiy50d8&feature=related Their song BlackCat (although I think I've heard it's actually a cover), since I seem to have a ton of trouble finding stuff on them.
Dr. Bombay; Bubblegum Pop, I completely forget where from though. Very fun if you like that kind of stuff. I particularly like Rice and Curry.
Seeed; German rap, I must admit I've only heard one song by them, Ding, but it was quite good.
REDALiCE; Japanese techno group. Part of it, ALiCE'S EMOTiON, does a lot of video game remixes. Running Dog and Taboo Tears You Up I like in particular, and the entire album of Oto no Ishi is great if you don't mind that it's basically a medley of remixes from the game Mother that runs for over an hour straight.
IOSYS; Japanese ...uh...something or other. They're really all over the place with the genre thing. They mostly do remixes of Touhou music though, and occasionally remixes of their own music. I'd recommend Hakurei Shrine Neighborhood Association Marching Song, Artificial Children and Eirin's Clinic That People Queue Up For. Border of Extacy is also good but I'm not sure I'd recommend listening to it in public, and personally I like the song 患部で止まらずそのまま奥まであんああん 〜 最後の優曇華院 ,but I suspect that it may cause hemorrhaging in some people.