As of today (9/30/99), Delta nor TWA flew the FLL-MIA route.
American Eagle/United Express does fly the SNA-LAX route, on EMB-120 aircraft.
USAirways Express (Piedmont Airlines) flies the Dash 8 on the BWI-DCA route, and USAirways flies 733s, 734s, and 757s on the BWI-PHL route.
There are no Crosstown New York flights, but it is amzing (to me) that airlines actually fly these routes, when you can drive!!!