Like anorexia, obesity, addiction to Warcraft, and fundamentalism, I think insomnia is a product of our culture. Rather than interpreting these various phenomena as "purely" psychological or physiological, a social view of U.S. culture as having certain toxic effects helps one not to blame oneself for various dysfunctions and addictions.
I am somewhat of a light sleeper to begin with, and stress means that if I wake during the night (to pee, because the dog needs to go out, because my son wakes and calls to me, etc.) it can be hard to fall back asleep. When I had Lane, I also had baby-related insomnia in a big way: by the time he slept through the night, I couldn't. A therapist recommended an excellent book, Say Goodnight to Insomnia and I recommend it heartily for the clear, calming, book full of good sense that it is. Really helped me to know I would not die of insomnia and that I could be ok in time. I also took benadryl, which had the lovely effect of giving me a solid 6 hours a night but dried up my milk so I stopped breastfeeding much sooner than I'd planned. (My OB should have warned me, but did not, dang it.) Some folks can't do the Benadryl/Tylenol PM type route because it makes them wonky for too many hours (or days), but at least it's not addictive and doesn't give you short-term amnesia and cause you to crash your car like Ambien! (I have friends who have experienced both!)
But I've found myself a new cure that works best of all: books-on-tape and my iPod. I have a bunch of books of light and frivolous nature (most by P.G. Wodehouse) on my iPod, and I simply turn them on very softly and listen when I wake in the middle of the night. Except for the harsh nightlight that is the iPod screen, it doesn't disturb my spouse beside me, doesn't involve altering my body chemistry, and can be used over and over. Between free downloads from the public library and iTunes, I've got wonderful radio plays and classic literature, silly comedies and mindless mysteries. I have new books that I haven't listened to for when I first lie down to relax me if I need it (instead of TV) and old favorites (especially Wodehouse's Blandings Castle tales) that I know almost by heart.
I find myself wondering if I'm the only one who does this. In any case, it really works for me.