I have discovered a really fantastic riparium plant.
Cyrtosperma johnstonii is a large aroid with amazing foliage. The arrowhead-shaped leaves have this wild pink, green and gold coloration.
The leaf petioles are also unique, with many curved thorns and a purple snakeskin patternation.
This plant does get to be large (<6'). This specimen is now about 30" tall, but it is growing four little suckering plantlets around the base. It should be easy enough to just snap these off and start new small plants as the main stalk gets to be too large.
The newest leaf is going to be larger and it looks as though it will have even more of the gold and pink coloration.