Join Date: May 2013
Location: Australia, Victoria
Salvinia, Water Lettuce, Amazon Frogbit and Duckweed are true floating plants, but you can also float Anacharis, Water Wisteria, Water Sprite and Hornwort. There are other plants you can float but these are the ones off the top of my head. As for rooted in the substrate you could go with Hygrophila Polysperma/Dwarf Hygro, Crypt and Vallisneria. You could probably put a small Anubias and/or Java Fern in the substrate just plant the roots not the Rhizome.
Some of these plants might grow to tall for your tank though.