My programming playlist consists of mostly

  – M83					Electronic/Shoegaze
  – Ratatat				Chillout
  – Eluvium				Ambient/Classical
  – Sigur Rós				Post-rock/Ambient
  – Mono				Post-rock/Ambient
  – Explosions in the Sky		Ambient
  – Air					Ambient
  – Brian Eno				Ambient
  – Godspeed You! Black Emperor		Post-rock
  – Jesu				Post-rock/Drone
  – Mogwai				Post-rock
  – String Quartet Tribute to Coldplay	Classical
  – Yongfook (Jon Yongfook Cockle)	Ambient

Mostly ambient, post-rock, drone, and chillout. Either no vocals or ambient vocals. About 280 tracks in total, about 25 hours.

Hit shuffle on that, and I have myself a killer well-mixed playlist in terms of variety, tempo, and genre selection.