Rotala indica (real one, not the fake rotala rotundifolia)
limnophila aromatica, ludwigia inclinata and some other plants
My favorite: Echinodorus Angustifolia vesuvius
Blyxa japonica
Cabomba furcat $1.5/stem http://www.aquaticplantcentral.com/forumapc/plantfinder/details.php?id=161Egleria fluctuans $15/stem (on the left, that is how much I paid for when I obtained it in Japan)
(The red Rotala macrandra 'Variegated' on the right is not for sale)
Didiplis diandra
"giant" saggitarria? Whatever it is, a nice background plant.
$1.5/plant