I am surprised that no one has mentioned Twelve South's "BookBook" case. I have had the iPhone 5s version for about a year and really like it. They haven't released the iPhone 6 BookBook yet but it should be out in a couple weeks or so. My iPhone 6 will arrive in about a week and I will get the BookBook as soon as it becomes available (I signed up for the email notification), assuming that they don't make some change to the design that I don't like.
The only thing I don't like about the iPhone 5s BookBook case is that it isn't quite wide enough to fit cash completely into the slot, meaning the cash stuck out a little and gets bent when the case is closed. This shouldn't be a problem with the iPhone 6 version. Otherwise it's great, with a hole for the camera and enough leather around the edges to protect the iPhone from drops. It was weird for the first few weeks, constantly thinking I forgot my wallet whenever I left the house. Now I can't imagine going back to a regular wallet.
Sorry, my iPad mini refuses to copy/paste, so I can't post a link. Check out the Twelve South website though.