Most corals will be fine in your tank. I'd avoid trying clams, but mushrooms, button polyps, sand polyps, gorgonians, cabbage corals, and colts should do fine. You'll need to make sure your feeding enough for the filter feeders, but otherwise you're okay. The tank depth is sometimes a concern, but I think the 55's are okay. Just make sure you have plenty of surface agitation (or the skimmer--does the same thing).
I wouldn't add any corals until you've finished adding live rock, and the tank has matured for a few months--6 is the minimum I recommend. Most inverts are sensitive to fluctuations in water quality and salinity, so once that's stable and easily maintained, you should be okay to add some more inverts.