That Was the Worst Christmas Ever! Also, my first Sufjan song period. Had it in my library for probably five years before I listened to a whole Sufjan album which is stupid.
picked up The Age of Adz finally on vinyl recently and babbled on about it on my YouTube channel a few days ago (along with 12 other vinyl pickups). I question whether he'll ever make another record like it (or track like Impossible Soul), but I'd love to see him try.