First, top it off with water. You've got a good 2 inches of no water on the top.
Second, you're gonna have to move those goldfish soon.. They grow too big for the size tank you have..
Third, PLANTS! Fake or real, they will make a great addition to your tank.
Fourth, get schooling fish (tetras, danios, etc.) and one "stand out" fish. I have 7 neon tetras(red, blue, silver) and a male tequila sunrise guppy(orange, yellow, white) as well as the "interesting" fish, kuhli loaches.
Fifth, I think you have too many rocks.. Get rid of some and incorporate some fake plants into it if you don't want to take care of real ones.
Here's some pictures of my 10 Gallon