Stuff from Dwelling of Duels[1] (Video game covers), artists that mix classical instruments with rock/electonic (like Sarina Suno or Yoshida Brothers), or movie/show soundtracks (Hisaishi Joe) - anything with lyrics is too distracting. And that's only if I know what I'm going to write, if I need to sit and think about something, I need silence.
[1] http://dwellingofduels.net/