I took an old army tent ($20 at my local army surplus store) and cut a section out of the corner. I lined it with a Delta airlines blanket (it's really soft, kind of cleans the screen when I put the tablet in there) and I made sure to have the embroidered logo face outward when I sewed it in.
My Nexus 7 has a sleep sensor
, so sewing a magnet between the canvas tent and the liner blanket that I robbed from an old hard disk in there will put the tablet to sleep when I slide it in the sleeve, and wake it up when I pull the tablet out. Pretty handy! It took some trial and error to get it in the exact right spot to trigger the sensor. The annotations in the pictures show what I mean.
I also sewed one magnet in the top of the flap, and one in the front of the sleeve so that it will snap closed and keep itself shut. I thought this was more elegant than a grommet or a button. Make sure the two magnets are rotated so that they have opposite polarity so that they will attract rather than repel.
Looks pretty snazzy in my opinion. The only thing it's missing is a big red cross logo sewn in the middle.