I can never remember the name of it, but I use the sticky stuff that is used to attach poster board to walls. I call it Tacky but I'm sure that is not the proper name.
Sticky-Tac? That's what we called it years ago. I think museum putty would work also. And there are other brands out now too, I recently bought some that was made by Scotch, they call it "removable mounting putty".