That site recommends the Phillip Pullman 'His Dark Materials' series which I haven't read, but which is almost as popular as Harry Potter. Also William Nicholson's 'The Wind on Fire', again which I can't comment on.
I personally would also suggest 'The Hobbit' by JRR Tolkein and you could then progress onto 'Lord of the Rings', and maybe 'The Chronicles of Thomas Covenant' series by Stephen Donaldson.
Something easier and shorter is 'The Shadowmancer' by GP Taylor which I've just read and my daughter has started. He has a new book out in 2004.
Or the 'Chronicles of Narnia' series by CS Lewis.