Another nod for Low. And as strange as it seems, when I battle insomnia I find I can sleep listening to Godspeed You! Black Emperor on IEM's. The albums I typically use are "Lift Your Skinny Fists Like Antennas to Heaven" and "Allelujah! Don't Bend! Ascend".
There's something about the chaos of GY!BE's compositions that calm my brain activity. Give it a try.