Business Card Holder
This can be adapted to any stitch pattern you like. Seed stitch, ribbing, cable, whatever. I used garter stitch because it's so stretchy and it worked out very well. I'm going to give instructions for that, but modify to your heart's content.
First you need to do a gauge swatch to find out what your stitches per four inches are on the yarn. Normally you find out your stitches per inch by counting your stitches per four inches and dividing by four, but since this piece is four inches wide, you'd be dividing by 4 only to turn around and multiply by 4, so don't bother with either and just count the stitches. :) If you come up with an odd number, add one. That's the number of stitches to cast on. For me, that was 20.
Knit the first two rows.
Knit half the stitches (10 for me) of the third row. Yarn over and knit the rest of the way across. So now there is one extra stitch (21 on mine).
Keep knitting back and forth until the piece is 5 inches long.
Fold the bottom 2 inches up and seam the sides. I used single crochet, but any seam will work.
Fold the top inch down, line up the button hole and sew on a button.
If you like, you can make the top inch a different color than the rest for a contrasting flap. Then you won't even need an ounce of a single color to get it done.