There are a few websites you can check before you read a book. If you know one I have missed, please let me know.
Common Sense Media-I like the rating system on the site. Members can give star ratings and reviews. It also covers TV shoes, movies, websites and music.
GoodReads-I just find the place on this website where I can see which friends give similar ratings to my ratings.
Shelfari-I like being able to add tags to organize my books. Also, I can see which books have the highest ratings for the day.
LibraryThing-I like that I can give 1/2 stars on this site.
Here is an observation from one of my emails:
I've conducted a teen book group at a public library for a long time now. A few years ago we were discussing genres and I was book talking a lot of books that weren't fantasy in hopes of giving the kids other choices. When they didn't take the bait, I asked them what it was about fantasy that they loved so much and their answer surprised me--They're clean reads. I hadn't thought about this before but realized they were right. And I applauded them for knowing what they wanted and what they didn't want. Some of them also informed me that was why they read books from the general section of the library, rather than the teen section--they didn't find as much of what would be objectionable material in the authors they were choosing.
When I got back into children's lit about 20 years ago, I would often hear authors say that an editor or publishing house had requested they take certain things out of their books because people wouldn't buy the book with those things in it. Now, I hear them say they are encouraged to add those things if they don't have them in their books.
I have been impressed with Common Sense. They don't pass judgment. They don't say "read this" or "don't read this". They simply state the facts AND then give questions parents could use in discussing the book with their children.