In case you aren't aware, the American film ratings (G, PG, PG-13, R and NC-17) are a voluntary system by and for parents. Not only do they tell people what is and what isn't appropriate for their children, depending on their age, they also give basic details of what type of content has influenced each film's given rating. Information on a movie's rating can be found in its advertisements, most film reviews and a special search-engine-powered website (www.filmratings.com). What more could a responsible parent or guardian ask for? How about MPAA Dan Glickman comes over your house and describes each new release and its assigned rating ... every week?
Unfortunately the man is just too busy saving the world from pirates of Pirates to do that, but he's going to do the next best thing: send you an email. Parents (and non-parents, I'm assuming) can subscribe to the new "Red Carpet Ratings" service, which sends out one email each week giving a rundown of what is coming out. The service is designed to keep (lazy) parents informed of each new movie's rating, though chances are they will also include plot synopses, which will additionally serve to market new family films (as well as other films for the parents to see on their own), even if unintentionally.