It’s the Chocolate Box square continued out into eternity--or until I run out of leftover skeins. Or energy. Alternating dark/light colors.
Using all solid colored partial skeins & leftovers in the house, and maybe a new one or two, mostly worsted weight.

update 4/11
You know your square might be getting truly big when it takes a half skein of Brown Sheep Lambs Pride or Cascade 220 to get around it. But I’m not ready to stop yet.

update 11/11/11
Finishing with a round of double crochet in every stitch and then a round of single crochet in ever stitch. Taking awhile, its a little over 5 feet square.