I continually see and hear the appelation "Shlita" attached to some people. Obviously, it seems to be a title of honor and distinction, but, oddly, my dictionary of reishei tevot does not list this one. What are the words of the abbreviation and what is the English translation?

You are right, it is Rashei Teivot for Shlita are Shyichyeh L'Orech Yamim Tovim Amen. In English - May he live for many good days, amen. It is usually attached to name of important rabbis.