I just tried the Silk with no sugar, and I really enjoyed it! It's similar to the plain Silk, but with no sweetness. I guess I didn't really notice how sweet the plain was until I did try the the no sugar one, but it was a fairly easy transition, and I suppose if you really needed to, you could a sugar substitute or something.
I just found it at the grocery along with the regular Silk, but I can't remember which of the local stores I found it at, but it was the first time I'd seen it. Maybe you can ask them to order it for you if they do not yet carry it at your local grocer.
http://www.whitewave.com/index.php?id=117&pid=37
I hope this helps!