We went through a short stage of nightime fear. We would read the Grover book - "Theres a monster at the end of this book" and we would go through his room and the hall getting rid of monsters. I made a little ritual of walking him around with a flashlight telling all the ghosties it was time to go outside and play. That really helped. We took all the fear out of them by talking to them as if they were silly playful friends that didnt belong in the house at night.
Also, Have you tried white noise? My son sleeps best to the sound of the fan. I point it away from him so he doesnt get cold. But the cold probably helps him sleep better too. He piles blankets on and buries in for the night.