I recently designed and printed an end stop switch for my RepRap after I broke one of my store-bought ones. It isn't 100% printable, it makes use of a pen spring and wires, but it has worked great for dozens of prints so far!
Here's the link: Thingiverse
This is definitly not the most practical end stop switch, as store-bought ones are realatively cheap, reliable, and long-lasting, but this end stop is more of the spirit of RepRap, and was a fun challenge to design and make.

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