I like to get one of each of my boys sitting on the same recliner year after year--someday I'll do a LO showing them each year, what their costume was and how big they were getting (although DS2 wouldn't sit for me last year...and almost wouldn't wear a costume either!)

I also like to get a picture of them walking down the driveway, ready to go trick or treating, because they are walking towards the setting sun.