Cressida Cowell: How to train your dragon, etc. all about a little viking called Hiccup Horrendous Haddock the Third.
These books are avidly read by both ds1 (9) and ds2 (7). They are very appealing to children (lots of cartoon-style drawings, wacky sense of humour, etc.), but are much better written than, say, Horrid Henry. At ?6 for all 3 books (save ?12) they'd make great presents too.