I have a 20 gallon too.

some neon tetras, mutant goldfish, algae eater..a siamese fighting fish..and 4 white clouds (lil "feeder" fish..but nobodys gonna eat them now)
plus like 11 plants.

its awesome. everyone gets entranced when they look upon my underwater utopia. you cannot resist it.
supposedly, contemplating nature puts you in an altered state. so, simply having an aquarium around keeps you altered, relaxed. heh...pretty fishies

the appeal of an aquarium is being able to play god.