I was told that beginners should get nothing smaller than a 55 gallon. Water parameters are more important in salt water tanks than freshwater, & its easier to control them if you have a bigger tank.
If I had a salt water tank, I would get a lion fish. They have to live alone or with other lions because they're very aggressive, but they're absolutely gorgeous & get HUGE. I think starfish & other inverts can live with them, though (don't quote me on that). & clownfish are nice as well.
Look online at websites like animal-world.com in the saltwater section & find some you like.