SIO2SD
In 2009, I decided my SIO2SD board needed a home, and an XM301 modem case seemed a natural place to house it. Since the prototype case was made, the design has undergone several refinements and now (optionally) includes a pass-through SIO connector on the back for "daisy-chained" devices. The SIO read/write LEDs have also been combined under the existing half-light, and the power light has been dropped altogether.
You can download instructions for building your own SIO2SD/XM301 here (PDF). Alternatively, email me for more information.