I think small Utricularia, Drosera or Pinguicula would look nice. They are all carnivorous plants and are great with fungus gnats. Utricularia can easily become a bit invasive, though. Pings are the best looking out of these in my opinion. They have green, succulent like leaves with bright purple/pink flowers. For any of the carnivorous plants, rain/RO/distilled water is preferable, although any water lower than 100ppm is fine.
Here's a list of South American carnivorous plants.