I found it appropriate to use picture of keyboards as headers. They are displayed randomly, so that no image provider can complain about favoritism (though I would make some headers display more often if I could).
So far, Xander is the only one who provided me pictures, but I’d like to make sure it does not get boring, so do not hesitate to contribute. The headers are 1000 px wide and 288 px high. If you are interested in sharing your own creation, you can contact me so that we figure out the details.