BG, here's a trick I've learned for this situation when my mind refuses to shut down.

Count sheep. REALLY. I'm not kidding. But, there's a trick to counting that makes it effective.
1.) Imagine the sheep jumping over the fence in great detail - the color of its wool, the shape of his eyes, nose, mouth, the greeness of the grass, the height of the fence, the speed of the sheep running, etc.
2.) Count each detailed sheep picture as the sheep jumps over the fence from 1 to 10 (or higher) and then backwards from 10 (or higher) to 1.

This is designed to use up both left and right brains so that it "crowds out" what's in your mind. Once you reach 0 sheep, your brain is done processing and it should be "empty" and will be ready to sleep. A lot of times, the brain gets bored with counting and would just fall asleep in mid-count.