Did you guys read his tank size? It's an 8 gallon cube! With the exception of a clown goby, none of those suggestions would work in that small of a tank! Clownfish need 20+ gallons (although I know some of you squeeze small babies into smaller tanks, they grow quickly), and a shark...seriously?
Your best bet would be a yellow goby or clown goby. They stay small enough for your tank and have great personalities from what I hear.