Coral calcium seems to be touted recently by certain health food junkies. They tout it as beneficial, especially for arthritis and osteoporosis. It also seems more trendy then the older oyster shell calcium.
As far as I have been able to find, there are not health benefits associated with coral calcium. In fact, like oyster shell calcium, it may be worse for you then plain old Tums because oysters and corals don't dissolve quickly; - the calcium is not available for absorption. Almost the entire supplement will just go through your feces.
I usually try to have an open mind about natural supplements but I also have to skeptical about results. Many people say that they feel better after a month of a particular supplement but they are no longer on it at the next visit. If they get psychological benefits from taking such things, I just let them spend their money.