I've collected a list of great books, and my kids are selecting what they want to read from that list. I think having a very good grasp of classical literature is vital for a full education.

Some lists of books are:

Random House

American Library Association BookList

Caldecott Medal Winners

Some interesting commentary on Banned Books also gives a list of good books.

And here is information on Project Gutenberg which is a download resources for books in the public domain.

Writers of the Future is a very good resource for finding new & brilliant science fiction writers.