Have you ever noticed that even though you haven't moved or bought a new car in years, every time you open your junk drawer you find another key? They tend to breed in dark places. This is a perfect recycling project. My key stash yielded a number of interesting specimens so I glued them onto a background and framed them.
May I rant a bit?
I don't trust glues. I've put together projects only to have parts pop off months later. Yet it takes chemical warfare and a blow torch to remove price tags. I understand that some airplane parts are even put together with glue. I think there are 2 kinds of glue; one for the commercial sector and one for us. Please manufacturers, trust us with glues that work!
Whew, I feel better now. Saying that, I have found that Goop is fairly reliable.
black foamcore board
heavy duty glue (Goop, E-6000, Liquid nails, epoxy)
Arrange keys in a pleasing manner. Adhere each key using a tiny bit of the glue. Allow to dry and frame.
Unless you use your glue every day buy the smallest tubes possible as no matter how tightly you screw on the caps, they always tend to dry out and there is nothing more discouraging than a large, expensive tube of hardened glue.