Brian,
I brought some stuff with me when I visited Cincinnati last summer. Many of the airlines will FREAK when you tell them you want to bring live corals on. I went on Delta, and you should check with the carrier you plan to fly with to see if things are different. If you try to check a cooler with corals they will REALLY freak.
Best method. Say nothing, and bring them as carry on. Tell the x-ray security guys exactly what they are and let them look at it, they will say 'cool, live corals' and allow you to got through. If they X-ray them it will not kill them.
The funny thing about all this is that I now ship corals via Delta Dash all the time, and they go on the same plane that everyone else goes on, but it is a long process to become a verified shipper (security checks, site inspections, etc., etc.).