Here's a
list of good plants in general. In terms of plants that are both safe for chams and will hold up well to a gentle shower, I would probably favor Schefflera (umbrella plant, umbrella tree). Ficus (fig) comes in good sizes and might be good - it's a good cham plant - but some drop their leaves pretty readily when experiencing any change in conditions - such as a sudden showering.
You probably already know this, but you'll want a gentle, lukewarm shower, with enough of the plant out of the flow of water for your cham to decide when to go in and out, and how wet he wants to get.