Assemblage 23.
In Strict Confidence.
Decoded Feedback.
Searchlight.
Bôa.
Die Fantastischen Vier.
DJ Lizard. <-- Unfortunately I believe he's taken all of his music off the web. If you can find It's Only Life or Oceanic View, those are both good trance-y songs)
Louis XIV.
Massive Attack. <-- They did the theme from House MD.
Múm.
Skillet.
Sweetbox. <-- Jade, the singer, did Real Emotion and 1000 Words from FFX-2 and split from the rest of the band, so I'm not sure if they're still considered obscure. Apparently this specific song is really popular in Korea.
SONIA. <-- Theme song for Tenchi Universe

I apologize for some that are really popular. Among my friends, these are artists that none of them have heard of and that I can categorize as really great