I've got mine in a binder sorted by my checklist. If I'm missing a card, then I put a blank slip of paper in there so I can see at a glance that I'm missing that one.
The only time this doesn't work is for the current year, or if you discover a card from years past that wasn't on your checklist originally. A bit of a pain to move things down, but it's the easiest way to organize?
