I'm on a mission to find plants that will work in a cage. So far, this is the only one I've got in there.
It's a bromeliad, which is safe for snakes to be around. It's an air plant, so it doesn't take root, and can be pushed around all the snake wants. It only needs to be misted once every other week, so misting the cage is enough to keep it living. It's about 8-10" in diameter, and can support the weight of my snake, though she's only 250g right now. She loves to crawl through the leaves/blades/whatever.
I've only had it in there a few weeks now, but if it works out, I'll try some other similar plants.