I'm a huge fan of the Oliver Moon books! I have a six year old boy who is a good reader for his age and so I was looking for chapter books that weren't too difficult to read and that were easy to understand.
For the uninitiated, Oliver Moon is a young wizard at Magic School and the books are all about the magical mayhem that he gets up to. In this book Oliver is landed with the terribly boring job of litter collector at the Festival of Magic Parade...so he decides that he should try to make his job more interesting, with the help of a small dragon that his little sister has recently found. Of course, things don't go according to plan at all...
These books have really hit the nail on the head! They are full of lovely humour that five years plus can easily understand and appreciate, and have lovely, short chapters that are brilliant for giving a real sense of accomplishment to a reader who's embarking on "proper" books for the first time. I think that one of the nice things about Oliver is that it is really easy for a young child at school to identify with him as he experiences so many of the everyday things that they, too, will experience. For example, there's a boy at Magic School who tends not to be very nice to Oliver...but luckily he usually gets his comeuppance in a way that makes my son laugh out loud. The book has simple little black and white illustrations throughout that add nicely to the story.
I would highly recommend the Oliver Moon series for any budding readers that are ready for short chapter books, or indeed as fun, light reading for more accomplished readers.