Elana Johnson who writes YA sci-fi and fantasy has begun to spread awe - awe and wonder is - awesome and wonderful? - no, it's a great idea.
The book and author I'd like to nominate is Ender's Shadow and Ender's Game by Orson Scott Card.
I read the books in this order; this is not the correct one - however, the mature writing in Shadow meant I had Bean adopted and made mine long before I got passed the end of page 5. The saga, too me, was whole and complete and I had no idea Game existed until I read the (lets face it who reads them) author's post. Have to admit I never read anything that comes before the title of "Chapter 1" :)
The books merge when Bean and Ender are both at the Academy together - they become two views of the same story as it unfolds. I enjoyed one book and I adored the other. I'm glad I read both - I learned a lot about how the writer's skills develop over time.