2006 Notable Children's Book by the American Library Association. An extensive list for all age levels.
Boston Public Library has several interesting lists
Good Books for Younger Boys Good Series for Young Boys
Good Books for Older Boys Good Series for Older Boys
Children's Book Council has a list of new books for kids. It's updated regularly.
The Database of Award Winning Children’s Literature has many ways to search for lists including age level, genre, etc., etc.
Kidsread.com has a list of Classics and New Favorites.
The King County Library has a list of "good reads" with age recommendations.
The Los Angeles Public Library has a variety of ways to look for summer reading suggestions--by age, by genre, award winners, by author, by series . . . Take a look.
The National Education Association created a list from an online survey of books that kids love to read.
National Endowment for the Humanities has a list of summer favorites sorted by grade level.
The New York Public Library has a list of 100 favorite children's books for a long list of genres.