We had lots of great discussion with my post about books and ratings. Thanks for all the comments!
As I mentioned, I'm all for sites that provide guidelines to books. They give us a heads-up on the actual content rather than slapping a one-size-fits-all rating. I'm not for ratings themselves because they're too subjective too be truly helpful.
Since that post, a few sites like that have come to my attention. I'm sure there are others, but here's a few to start out with:
Good Clean Reads
A great site mentioned in the comments by its creator, Kim, is Good Clean Reads. She's developed her own system to "rate" books. I put that in quotes, because it's not so much a rating system as it is a way to clue in readers on content. (This brings me all kinds of joy. It's just what we need!)
Each "rating" consists of three numbers, from 1-5. The numbers represent sexual content, violence, and profanity. Put the numbers together, and a rating could look like this: 2.1.3.
Kim herself is careful to point out that even this system is subjective, but her system is just about as good as it gets.
This site uses a simpler rating system (very easy, but probably not quite as effective as Kim's), that rates the level of content from "None" to "Dirt." I didn't know until I found Rated Reads and poked around that my good friend Heather Moore is one of their reviewers. One thing they have going for them is that they have a pretty decent-sized archive.
Parental Book Reviews
This site falls between the other two on how complex their rating system is. Parental Book Reviews uses a 7-level scale from "none" to "extreme," giving a rating on four content areas each: sexual content, profanity, violence, and "other notables," which I appreciated, and which includes things like underage drinking or other elements not covered in the other categories.
This is a sister site to Parental Book Reviews, and it's aimed specifically at young adults. Fellow writer Braden Bell pointed me toward a brave and insightful post there, written by a mom, about sex in youth fiction.
It's long, but worth the read. Read it and discuss it with your teens.