Stems plants are the plants that consist of a thin vertical stem that can branch of into other stems. If you trim the top off, 2 new stems may replace it, adding volume to the plant.
Rotala rotundifolia looks good and seems easy to grow.
I'd recommend crypts. It takes awhile for them to get started, but then they take off, and look fantastic.
I've had great success with Ludwigia as well.
