You can look around your local pet/fish store(s) and find some colorful or nice looking guppies, and get two of those. You could also get 3 corys (corydoras) they are catfish and are really cute and they can be fun to watch. If you get corys make sure you don't have big rocks as your substrate (the gravel/sand at the bottom) because it could damage their barbels, which they use to find food.