There are some nice beginner corals you could start with such as some soft corals and LPS. I'd definitely stay away from the sponges, as they often aren't able to be maintained in a tank, needless to say a 10 gal where it can turn disasterous over night. Some good corals to start with are mushrooms, zoanthids, star polyps, xenia, and toadstool or cabbage leathers. There's a wide variety, but still you must take into account the lighting you'll have on the tank and rockwork so you can have different placement levels. Take a look at the Coral Profile page 1979camaro and I'm working on. You'll get a good idea of what corals to choose from and the pros and cons. For lighting, I would suggest for you to get a 96W 10K/actinic 50/50 fixture, as you'll have plenty of lighting for whatever corals you'd like. With some interesting rock work and a good design, you can support whatever corals you'd like, within reason of course.