I recently finished a lovely lacey cowl. The pattern is free on the Without Seams blog, its easy to follow and gave instructions for several yarn weights. (download the pattern here)
I used Blue Sky Alpaca Melange in Huckleberry, which is a gorgeous heathered sport weight yarn. Besides having my crochet hook split the yarn on occasion, I would say it worked up quite nicely.
The detailing of the pattern is great, a bit lacey and a bit ribbed. See below.
