I'll second the Harry Potter books -- I've been reading the Sorcerer's Stone (electronically) in Portuguese after working through Duolingo. It's nice because I am familiar with the story and there's loads of new vocabulary, which I look up (after guessing) by switching to a translation app.

If you're on iOS, the built-in dictionary app will give you Spanish->English.

What translation app do you use (unless it's the built-in one)?

Yes! Rereading a (good) book you've already read is an excellent learning technique. (Mine was Dune.) Your foreknowledge provides plenty of context, something which is often lacking in more artificial exercises.