I really love the mirroring of Voldemort and Harry throughout the entire series. They really must be one of my favorite protagonist / antagonist duos. I don't want to spoil the series for anyone who hasn't read it but I recommend it on the sheer opinion that J.K. Rowling did a fantastic job with the characters.
Here's a quick piece I did based on Harry / Voldemort in the 5th book, Order of the Phoenix. Not a book cover for once, just a concept piece.