Great series of books for older children to read (8+). The stories focus on Hiccup, a Viking boy who loves dragons, and details his exciting adventures in and around the Isle of Burke where he lives with his dragon Toothless. There are also audiobooks read by David Tennant which are really excellent – he does an amazing range of accents for the different characters which can keep the kids (and adults!) happy on a long car journey!
By the way, the books are not quite the same as the films/TV series (which are based on the books).