This photo of John Hakim's 5.5g mini-reef aquarium pictures a great close-up shot of his White Stripe Maroon Clownfish and Cleaner Shrimp, with an Xenia coral, Leather Mushroom, Green Mushrooms, and a Plate Coral.
Smaller tanks make great Do It Yourself (DIY) Projects. They are fun, easy, inexpensive and go together quickly. Just modify the DIY 55g Glass Aquarium Plans to meet your needs. There are a number of Canister and Power Filters and Mini/Nano Reef Tank Lights which will allow you to keep corals in your new tank.