http://www.thebookpeople.co.uk/ – Reasonably priced boxed sets of fiction and non-fiction. Also good for activity and resource books.

http://www.redhouse.co.uk – Wide range of fiction, non-fiction, activity and resource books.

Kids at Random House – Interviews with favourite authors, loads of links to authors sites games & competitions and dowloads. Grown Ups section has resources and guides.