There are nights when the brain just doesn't seem to want to shut down. Just too damn many things racing around and you really can't put a finger on any one of them.
Thanks to the miracles of modern technology, I've found what seems to be a dandy solution, one that doesn't require medication. I get into bed and then I reach over and turn on my (relatively cheap) Nexus 7 tablet and watch a TED Talk. Somehow that seems to focus the mind, eliminates all the clutter, and leaves you with some powerful thoughts that, as you relax, carry you into sleep.
Things like this talk by Juan Enriquez, founding director of the Harvard Business School Life Sciences Project, discussing the evolutionary transition that mankind is at right now, a transition that could well mean your grandkids or great-grandkids will be an organism much different than you.
You might want to try it. Works for me.