Giant val is a good tall plant then again all vals are good in height so I would do some research on types of Vallisneria, giant hairgrass may as well get that good height in it after a bit. With all that driftwood I would say tie some java fern or anubias (large species) to them, do you have pics of them to give us a better mental image? I honestly don't know about many true tall plants. You may be able to get some Tall Rotala (species) but I don't know much about that plant. I've seen it get really tall though so, another suggestion is pearlweed, it can get really tall and is also a low tech carpeting plant great for beginners.