A few years ago (2011/2010, not sure) I sent a letter to Ariana Grande's fan mail address. She replied 2 months later with a hand written note (lost it, sadly) and an autographed photo. Didn't even send her a SASE or photo.
One of my favs I've gotten, just 'cause she was so sweet. Kind of sad she doesn't do autographs now and is a bit snobby.