et voila, finished wristband:

 

Here's the basic recipe:

Yarn: about sock weight, not sure on the yardage but it doesn't take a lot.

Needles: I used size 0, which means most people would use a 1 or a 2.

Stitch Instructions: 

C6F = slip first 3 sts to cable needle and hold to back, knit next 3 sts, then knit 3 sts on cable needle.

Instructions:

CO 16 sts.

Rows 1 and 3: knit 3, purl 2, knit 6, purl 2, knit 3.

All even rows: knit 5, purl 6, knit 5.

Row 5:  knit 3, purl 2, C6F, purl 2, knit 3.

Repeat rows 1-6 until the wrist band can be wrapped around your wrist and overlaps itself by about 1/4".  

Place button hole:  

When you get to row 5, instead of cabling place button hole as follows:  knit 3, purl 2, bind off 6 sts, purl 2, knit 3.

Next row:  Knit 5, CO 6 sts, Knit 5.

Finishing:

Next row: knit 3, purl 2, knit 6, purl 2, knit 3.

Knit all sts next 4 rows, then bind off all sts.

Weave in ends, and wet block wrist band.

Once wrist band is blocked and dry, wrap around wrist to determine proper button placement.  Sew on button.  Ta da!

ETA:  the garter stitch along the sides has a shorter row gauge than the cabled center, so in order to make it more even, I added short rows to the sides once for every cable repetition.  Starting with row #1 on the second cable repetition, I knit the first three stitches, turned the band, knitted back over them on the opposite side, then turned again and knit them a third time before going on to the purl stitches.  when you get to the end of that row, turn and knit the first three stitches of the next row, turn again and knit them back the other way, and then turn again and knit that row as usual, including knitting the first three stitches a third time.  If you have any questions about this, feel free to comment or email me.  This is an elementary short row technique, and it puts extra rows into the side to compensate for the difference in row gauge.