It is easy to make a case out of an Altoids tin for the Raspberry Pi model B:
Here are the steps, it takes about 10 minutes if you're handy with a dremel:
1) The trick to getting the board to fit inside the tin is to drill a small slot towards the bottom of the corner of the tin where the LEDs go (lower left corner). This allows the corner of the board to protrude a few millimeters through the corner of the tin. It also conveniently provides a perfect side viewing port to see the LEDs.
2) For access to the USB and ethernet ports, trim out about 70% of the left side of the tin and cover (from the bottom of the case to the top); this includes going around the top left corner by the top of the "A" in Altoids, to the end of the radius but not all the way to the hinge) . This can be done entirely with a drill if you're patient or with a drill and tinsnips.
--note: there will be a 1cm section of the left side between the hole from step 1 and the top-to-bottom cut from step 2. You want the edge of the board between the USB ports and the LEDs (where one of the board mount holes is) to abut this section of the tin so that there is "extra room" in the tin on the SD card side -- this will ensure the GPIO pins are not occluded by the radius of the tin on that side.
3) Drill 2 holes in the front for the RCA and audio jacks (the top third of the RCA hole will also pass through the cover).
4) Cut slots for the SD card and power cord on the right side (make the power hole large enough to accommodate the plastic around the male plug, not just the metal part; this hole will extend into the radius of the top right corner).
5) Drill a slot for the HDMI cable.
--note, the lip of the tin's lid will not require cutting for the SD slot, the power cord slot, the audio jack slot, the HDMI slot nor the LED corner access slot -- all of those holes are below the lid when it's closed; only the RCA jack, ethernet and USB access holes will impinge on the lid itself.
6) Drop a plastic gift card into the bottom to insulate the board bottom from the tin bottom.
--note, only the bottom requires insulation; the sides are fine and the metal HDMI, RCA, USB and ethernet ports can all contact the tin without worry; the audio jack is plastic and poses no issue while the SD and power connectors are nearly 1 centimeter inside the tin so pose no worry. Nothing but the USB and ethernet ports will contact the closed tin lid and they are fine to touch it.
7) Insert the Pi (with no connectors and no SD card) by angling it into the RCA jack hole first, then drop in the HDMI side of the card (you may need to spread the tin a few millimeters by hand to accomplish this).
8) Install the SD card and connect the connectors.
9) Simply open the tin lid for GPIO pin access; alternatively you could cut a slot to the right of the RCA jack to run a ribbon cable through.
-- note, no mounting screws are necessary at all.
-- note, both hinges remain intact and unaltered.