1WPG plants...
Anubias
java fern
java moss
most cryptocornye species
Egeria densa
Egeria najas
Bolbitis
Pennywort (grew for me anyway)
Marsilea hirsuta
E. tennellus
Some amazon swords
Vallis (perhaps, it grows for me at 1.4WPG, never tried it lower, but I don't see how it wouldn't)
Aponogeton species (depends on the species)
Some hygrophila species
Probably Lymnophila sessilifolia (Not as tricky as cabomba)
I bet Nymphaea would grow well too. Mine grew leaves in a bucket choked with duckweed)
You can expand the list quite a bit if you add CO2 and ferts, though the plants above will grow well without it, maybe some fertiliser when you feel like it and a rootab for the rootfeeders.