There have been several previous threads on this topic, which I have tried and failed to find.
We had the same problem (and it is a problem!) and can recommend the following:
For newly-fluent readers:
Mr. Majeika books by Humphrey Carpenter
Sophie books and anything else by Dick King-Smith
For properly fluent readers:
Narnia books by CS Lewis
Harriet the Spy (can't remember the author)
Journey to the River Sea and other books by Eva Ibbotson
The Thief Lord and other books by Cornelia Funke
Little House on the Prairie by Laura Ingalls Wilder
Noel Streatfeild: Ballet Shoes etc.
Harry Potter (not for sensitive kids, maybe)
E Nesbit books such as The Phoenix and the Carpet
Roman Mysteries by Caroline Lawrence
Enid Blyton (people can be v. snobby about this, but they make great bread-and-butter reading)
The Hobbit by JRR Tolkein
The Penguin Classics series, which includes lots of boy-friendly reading like Treasure Island and Beowulf.
Classics such as the Greek Myths etc. are also great and make good present requests. Actually I have let my dd read Jacqueline Wilson, as I think the stories, although challenging, are ultimately very positive. Wouldn't let her near Melvin Burgess etc, though.
Can I also plug (again) my favourite kids' mag, Aquila ? This is not only good reading in itself, but contains book reviews to give you new ideas.
Roisin, has your ds tried Moonfleet, by J Meade Faulkner?