ferns: java fern, needle leaf or narrow leaf java fern, african water fern (aka bolbitis fern) phipine java fern (suppsoedly gets the tallest). Regualr java fern is the most common but its not the only one!
anubias (omg so many use to have a huge collection of these!): coffefolia, broad leaf, angustifolia, afezelii, lancolata, minimia, hastifolia, congensis (aka heterophylla), barterie, nana, nana var narrow leaf, stardust, nana var petite (also just called petite), micro (omg so damn cute and tiny but hard to find), gold, marle, snowwhite/snow/snowflake (multiple names for same thing, mostly white leaves)
most expensive and harder to find are the bottom 4, the snow white ones can go for over $100 for just a few leaves. Nana on the other hand is typically $5.
Both java fern and anubias are rhizome based plants (its a horizontal stick taht roots and leaves grow from) DO NOT EVER BURY THIS it will rot the rhizome and kill the plant. Most people tie these plants to decor/rock/wood, roots will eventually attach themselves to that item (don't tie too tightly, it would be light cutting blood flow off to your limb).
Mosses (another with many varieties most common first): java, chirstmas/xmas, flame, singapore, weeping, christmas mini, rose, rose mini, fissendens (several in this sub family cant recall all their names), triangle,.. I'm sure I'm forgetting some..
Attach mosses with thread or fishing line, they will eventually grow roots and anchor themselves, you can even cram hem in crevices of wood or rocks.
Marimo: NOT a moss, its actually a specialized form of hair algae, needs very little light, too much light lets other algaes grow on it, you cannot use aglaecides or you will kill the marimo (bleach, peroxide, Excel, other algae killing products), only way to remove invasive algae is by hand/tweezers.
Some others:
Anacahris, hornwort, water spite, wisteria: floaters that can be planted, the last two prefer closer to medium light but some say they've grown in low light.
Dwarf hair grass, micro word, mini micro sword, hygro tiger, hygro compata, hygro angustifolia, several other hygros I can't recall atm 'grasses' and stem plants that can grow in low light though they tend to prefer medium lighting (all hygro plants are potassium hogs: if you see pin holes in leaves they need a potassium supplement).
Its late I can't think of any more to slap up here right now.. if I remember any others I'll post them.
My vote is for anubias, LOVE that plant, slow grower but durable as long as the rhizome is not covered or damaged (they can unfortunately suffer from a spreadable disease called "rhizome rot" though, if you want more info on that let me know.. I lost my huge collection to the disease so I sadly know a lot about it).
edit: oo I always forget crypts >.< they are another good species with several varieties, though some are more medium light than low light plants.