Knitted Lace of Estonia and chose the Lilac Leaf Shawl. It is rectangular, which is what I had in mind, and it uses about the right amount of yarn. Hopefully it will use up what I've got. Mine will look a bit different, since my yarn is a light fingering weight instead of the lace weight the pattern calls for, but it should be lovely.
Already it's coming along nicely. I'm happy!