Have you ever tried meditation? An hour of focused thought before bedtime might be enough to calm your thoughts, and maybe induce a deeper sleep. It seems like you're stuck sleeping very lightly, which is normal for a lot of people (many of my family are light sleepers) but not healthy if all you have is nightmares.
Also, if you watch movies or tv before sleeping, you'll be more likely to churn up dreams and sleep lighter. This might also happen if you're active just before bed: When I was waiting tables, I had anxiety dreams about the job every night after work, probably because I'd pass out as soon as I got home.
There's also lucid dreaming. I've read that it can be used to work out problems, though I'm not sure about nightmares.
The only other option would be to try different sleeping medicine. Herbal teas, aromatherapy. Or maybe something stronger that you'd talk to a doctor about...