I've used a 'white noise' for both my boys and for the most part it works like a charm. Sometimes we put quiet music on but the white noise works best for us. To achieve that I use a humidifier fan, I just happen to have a loud one, but without the water in it. You can also purchase a sound machine at Amazon or Babies r Us but the volume on them isn't that loud, at least on the one I have. We do night lights as well but not too much light as it tends to interfere with sleep.
If it's monsters he's scared of get a small water bottle at the drug store and put a cool label on it that you can make on a computer indicating it's monster spray and then fill it with water. He can spray the monsters, hopefully he doesn't open it up and dump it out, and it makes him feel powerful and in control of his fear.
Another good rule that I've used is minimal words. I'll usually do a 'shhhhhhing' sound and say we'll talk about it in the morning.
If he has a lovey or snuggly thing that can help. Sounds like he needs to learn to put himself back to sleep, in his own bed without your help (my personal opinion of course, but do what works best for you). I've had success with the book The No Cry Sleep Solution by Elizabeth Pantley. Just keep in mind you need to stick by whatever pattern you choose to create and it may take a while but it does work. It's a nice short book and easy to read.