clipped from: www.knittersreview.com   
Here is a method that I learned in a lace class several years ago with Russian knitter Galina Khmeleva: purl the first two stitches together, then loosen that stitch up and place it back onto the left needle. Do the same thing again...purl the loosened stitch, now the first stitch on the left needle, together with the second stitch. Loosen it up and slip it back over to the left needle. Continue purling 2 together and slipping the loosened stitch back to the left all the way across. Pull the end through the last stitch left. I think this works by knitting two together and slipping back, too, but the purling gives a lovely, stretchy edge that I guarantee will not be tight!