Frill, Hornwart, Java Moss, and Water Lettuce could all work.. They are all floating plants, and the first 3 I listed you could wrap around driftwood and other decor. I am sure there are lots more available that you could use to a similiar effect as well.
I am not a planted tank wizard by any means, but I was under the impression that most rooted plants will 'sufficate' under the compaction of sand?
Java Fern can get fairly long, but it also spreads.. Depending on the lighting/growth regimen, you will get different 'growth' styles, if that makes sense. Longer, less intense lighting tends to grow long stringy plants.. and Shorter, more intense lighting seems to grow thick broad-leafed plants.
What I plan on doing is dividing the corners of the tank with slate, and in the back corners use a mixture of Florabase and Ecocomplete. In the foreground of the tank, where the display driftwood will be, I will be using a layer of sand. In the sandy open-water area, I will have no rooted plants. All the larger swords and grasses will be in the corners or the far back of the tank where I strategically placed the Florabase/Ecocomplete..
Hope that helps some
