Posters and other large visual aids. We have maps and a few other things on our wall all of the time, but we have certain posters we use for HSing but only in certain units. I don't have a problem with where to hang them, but storing them is awkward. I have yet to find a solution that works well for me.
We do a HS portfolio every year (required in my state) so the best artwork samples go in there and I keep those. During the year the kids put their stuff in one of those large Alex accordian-style art portfolios. I have a file for each kid in my personal filebox (stuff I access regularly) and keep little paper mementos in there.
Mama to DS-2004
DD-2006
and a new addition-ds born march 2010