As Grinity mentioned melatonin can be a big help.
We just got this worked out with DS5. He has always had trouble getting to sleep. He would spend hours in bed quietly whispering to himself about ideas and events. We tried everything suggested in this thread and elsewhere and it just didn't work. I could count the number of times between age 2 and 5.5 when he got to sleep in under an hour and a half on two hands. After Christmas it dawned on me that this wasn't really a behavior issue but a sleep disorder... We started giving him ~200micrograms of melatonin(half a pill from Trader Joes). Now he lays down after stories and is asleep in under 10 minutes every time. If we skip the pill, it is the old routine until we give him the pill. This has been a miracle drug for us. One disclaimer, DS is 2e(either asd or add) and these groups are thought to underproduce melatonin so your results may vary. Regardless, its cheap and easy to try.
