The United States Conference of Catholic Bishops (USCCB) maintains a movie review and rating system.  The archive is located at: http://www.usccb.org/movies/movieall.shtml

I find this more useful than the MPAA system to determine whether certain movies are appropriate for children and I would love to see a field for the USCCB rating added.

The classifications are as follows:

A-I -- general patronage;
A-II -- adults and adolescents;
A-III -- adults;
L -- limited adult audience, films whose problematic content many adults would find troubling.
A-IV* -- DISCONTINUED RATING. Originally adults, with reservations (an A-IV classification designates problematic films that, while not morally offensive in themselves, require caution and some analysis and explanation as a safeguard against wrong interpretations and false conclusions);
O -- morally offensive.

* Archived movies rated A-IV should now be considered as if rated L.

Agree with llmoelleb, there's US TV ratings, some US anime releases have their own ratings where do we start and where do we stop?

The USCCB ratings are really just a point of view as they aren't 'officially' used for film/dvd releases. They also have a  search engine for those that want to read what they have to say.

I guess they aren't horror film fans though, although they do recognise innovation and technical achievement