Growth Chart! $35 - fabric growth chart (do one for each kid and give to them when they grow up)
oversize ruler growth chart- vinyl decal. perfect first birthday present- you supply the board.
Old School Ruler Growth Chart - I would just put our last name on it though, then all the kids could be on the same growth chart.
"Put something like this up in each classroom or a large one in a hallway to show off work throughout the summer." -- We made something a little less fancy than this with string, ribbon, thumb tacks, and clothespins. The kids loved showing off their work, and the parents loved getting to see everything too.