Luis Contesini's 6g Nano Reef Tank contains a Percula Clownfish, and is loaded with an array of both soft and hard or stony corals.
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.