If natural remedies have failed to work (i.e. melatonin, exercise, etc.), I take Trazadone (prescribed). It's an older anti-depressant (I have mental health problems), but it is prescribed now-a-days as a sleep aide. It works well for me, and it's often used as a PRN (prescribed as needed) after a week or two of taking it, and it's non-habit forming.
I've also heard good things about Ambien, but I have never been on it.