Since my son seems particularly sensitive to movies, Common Sense Media has been a huge help. I've found their age ratings to be spot-on for him. And they rate chapter books as well as movies. Now when he's interested in seeing or reading something new, he tells me to go look it up, and we both accept what Common Sense recommends. It's a win-win for our family.
Thanks to Greg Robbins on Flickr for the use of this Creative Commons photo.