K.L.
Hi K.,
Don't forget to give him ways to handle his fears also, as well as the comfort he gets by coming to bed with you or else you may have a 7 year old in bed with you before you know it... :)
I've heard all sorts of ideas and babycenter.org has great posts about this... one was filling an old spray bottle with special "monster repellent" or whatever it is he's afraid of... and taking pains to spray down the room before bedtime (with water of course, or something with color that won't stain carpet or walls).
We all have fears and my little one, 2, was afraid our shadows for a bit... but once you talk them through it and show them what it really is, you can help them so much to deal with those fears. I was terribly afraid of the boogey man at 10 years old... and was an avid reader who thought everything I read could come true, so active imaginations can be good but also lead to lots of phobias. Remember to help your 3-year old to "name" his feelings, to validate them as totally normal and to help to give him ways to sleep in his room, knowing it's "monster proof" or "fear proof." At 3, your son still thinks that you are invincible, so use that to your advantage!
Good luck!
K.