I recently discovered this place:
http://www.gaylord.com/
Don't be intimidated by the name... it's not a gay pr0n site or anything.
It's a library supply house. They have a huge catalog of equipment, furniture and archival materials. There's lots of stuff that might be handy for collectors, like display stands, shelves and archival boxes.
Most of it's pretty expensive, but it's cool nonetheless. They typically deal directly with libraries, but they'll sell to private people as well. I just bought some photo sleeves from them to store game manuals. I'd love to pick up some of their magazine/CD racks too, but that's beyond my budget.