You could also pick up stitches at each end and knit a border or edging. You can find borders and edgings in some stitch dictionaries. There are some free edgings below:
I happen to think that lace borders and edgings really add something to a lace shawl. Edgings have to be knit sideways to the main shawl. You can either knit them separately and seam them to the shawl or attach them every other row on the WS by knitting the last stitch of the edging together with a stitch from the shawl end.