We gave my son a Kindle for Christmas. I asked my husband how many public domain books were out there that he could now access for free. "About a million," he said. "Most of them you've never heard of and wouldn't want to read."
My son did find something he wanted to read right away. The New American Oxford Dictionary. It comes with the Kindle.
"Mom, it has word origins!" He was so excited. He read me entries while I cooked Christmas dinner.