I know only posters and t-shirt designs are being submitted, but it would be awesome if Valve sold REAL Mann Co. keys! I designed this in CAD (Autodesk Inventor) and got it 3D printed in gold plated steel. This gold one is about the size of a regular key, but the model can be scaled before printing. More information at:

https://www.shapeways.com/model/934942/tf2-mann-co-supply-crate-key-small.html?materialId=39

A bigger one I printed out of plastic: https://www.shapeways.com/model/870510/tf2-mann-co-supply-crate-key.html?materialId=6

http://www.youtube.com/ikonakona
http://ikonakona.deviantart.com/