OK, if we concede that El Cortez would be first on the list we have to concede hotel expansions and remodeling as long as the "feel" of the casino is the same as the original. That means that even though Luxor changed EVERYTHING within a year or two of opening it still "feels" like the original. So if someone wants to see "original" casinos with the "feel" of when they were built I'll expand to ten casinos in case we need to eliminate some. I think I'll stick with downtown and the strip. My list so far would then have to be:

El Cortez - 1941
Sahara - 1952
Riviera - 1955
Fremont - 1956
Tropicana - 1957
Four Queens - 1966
Circus Circus - 1968 (Or has it changed "too" much)
Western - 1970
Plaza - 1971
California - 1975

I think Caesars and Golden Nugget have changed too much to be on the list. Let the debate continue.