Low stem plants are pretty fail proof. these include brazilian penny wort, Anacharis, Naja grass, water wisteria, water sprite.....
Floaters like salvinia and duckweed also do not require high levels of light :) Dwarf Water lettuce can keep the water clean by mechanically filtering the water with their long bushy roots.
I have many many snails in my 2.5 gallon tank :)