Older kids may balk a little when you make them read over the summer, but they should read. My kids need to read 30 minutes a day. That doesn't take much time out of their bus schedule. Allow tweens and teens to pick out their own books. This will allow them to read what they want to read, making it a not such a "chore." You may even be surprised at the books they choose.
Teens, leave me a comment on what your favorite book is so others can get a copy and read it, too!
Here is a list for the tweens and teens. Again, this is a very short list, however, some of the suggestions are series. Follow the links to Amazon on the Book Links page for easy ordering.
Lord of the Rings
A Wrinkle in Time
Anne of Green Gables
Chronicles of Narnia
Little House on the Prairie
Tale of Two Cities