These days, I'd usually listen to either a Dungeon Synth playlist (like Mountain Realm, Atrium Carceri, Witch Bolt...) or I'll listen to my doom/stoner/psych playlist (Mars Red Sky, Colour Haze, Earthless, Kikagaku Mori, Youngblood Supercult...).

Also, there are a few Diablo Lo-fi mixes made by blizzard that really get me in the mood of writing. Tristram theme Lo-fi is also sick.