Has anyone been to the Museum of Useful things in Cambridge? Unfortunately it's now closed, but it used to be a combined store and museum, with old and interesting gadgets displayed in cases and above head level around the store. It's the first thing that came to mind when Ben proposed a HacDC museum. The Museum of Useful Things still exists online, but primarily as a store. I couldn't find much on their site about the things in their collection, but there are a few pages (Example).
One thing that I liked about the physical store is that they often displayed old and new versions of the same product (with the new version available to buy). For example, this staple-free stapler was displayed under a model that looked more like one of these guys.