I was wondering... what plants can be grown on objects instead of in
substrate? I already know of java moss and java fern; any others? I'm
looking for non-floating plants, btw.

African fern, aka Bolbitis. All the varieties of Anubias. There are other
mosses, too, like Christmas moss and willow moss.

Amano covers rocks and driftwood with Riccia, by tying it with fishing line. I
don't think it attaches by itself, but it does well grown that way.

Leigh

http://www.fortunecity.com/lavender/halloween/881/