Persona games OST by Shoji Meguro. They are really versatile, they are really pleasant, they are great to listen to when you need to concentrate on the drawing or to feel free and careless and like you're having summer vacation in school. There are just enough beats in them, giving you just the right amount of wish to tap your toe or sing along.
Blind Guardian. Amazing metal, amazing nerd references. Of course you want to listen how Feanor fucked up everything in Hansi's voice!
Jeremy Soule. Well, this guy is not metal, nor does he sing, but his tracks are something I am literally listening for hours on a damn repeat, they are too good. He made music for Neverwinter nights, Harry Potter, Elder scrolls, etc., etc. Perfect background music, nothing else to say.
Susumu Hirasawa. Okay, Hirasawa is not for everyone, but he is basically the only techno musician I listen to, because his music sounds special, just perfectly balanced techno. Hirasawa's songs are really powerful, each in it's own manner. He can do crazy, he can do battle, he can do a tear-jerker.