My co-worker has this tank on her desk. She has a single dwarf gourami in it. She used to have guppies but they were mixed sex and kept having babies and eating them and she couldn't deal with that.
Tried more than the one gourami but he was too agressive for more fish. Remember, it's only about 3 gallons US or so (less if you consider the gravel, decorations etc inside the water), and if a dwarf gourami or male beta is about 2 inches that means you really can't put more fish in it without the fish feeling cramped and getting territorial.
But her aquarium is so beautiful it's what convinced me to set up my new 50 gallon at home. I liked the way hers looks so much.
-Nerwign