Plants that don't need roots in substrate

java fern and anubis will work

Anubias always work well for me. For some reason I can't get java fern to grow for me but it's supposed to be an easy plant.

Java fern and an u bias both work well, you can attach them to the wood or rocks with black cotton thread, or something similar, that will hold it in place till the rhizomes attach themselves.

Java fern and nearly all mosses will work. You can tie or superglue it. Mosses you can get effects depending on how its attached just be careful as I find most moss just ends up everywhere and can grow relatively rapidly once it takes off. Java moss is the most common but flame moss and xmas moss are common in my lfs amd occasionally fissidens (spelling?) Which looks amazing but ive had bad luck with

You can also tuck the base of java fern, or aubias in nooks of driftwood and roots will eventually adhere to the wood giving aquarium awesome look.