Oxford Owl is a great website for free e-books.
Stories always available!
Many of the stories are based on the Biff, Chip and Kipper characters.
Please note that the lower levels of books are not phonetically-decodable so you may need to help your child with some words.
(In school, we use Read Write Inc books which are phonetically-decodable: these are the ones we send home in Reception and Year 1).
The website also recommends books eg for Christmas.