This pdf file includes a couple different charts for creating a block ND. The first two are simple patterns for intarsia or duplicate stitching in two different sizes.

I really love the double-knitting version… if you simply follow the chart you end up with a completely reversible design. If you’ve never done double-knitting before, the video on this page is helpful: http://www.knittinghelp.com/videos/advanced-techniques This chart looks particularly funky because the pattern is not symmetrical from left to right, so I explicitly included the stitches for the front and the back of the fabric in the chart.

Here are a couple finished objects using these charts:
http://www.ravelry.com/projects/mariamaria/notre-dame-bab...
http://www.ravelry.com/projects/mariamaria/felted-reversi...