If you sign up for a Discover It card before the end of this year, they will double your cash back during your first year of membership (1% x 2). They also have a promotion through the end of 2015 where they will give a 10% cashback bonus on in-store purchases made with your Discover card using Apple Pay (including the Apple Store, of course) for up to $10,000 in purchases. That ends up being either 20% or 22% cash back after all is said and done (I was told that the 10% is instead of the base 1% reward, although others have been told it is in addition to the base 1% reward). You can also receive a $50 referral bonus (which may doubles to $100) if you can sign up for the Discover It card through a friend's referral, but that's just icing on the cake (I can PM you a referral link if you would like one). I am waiting for my card and plan to buy a 6S after I get it... I confirmed all of this with the Discover customer service rep in chat, but you can as well if you need the reassurance.
