I've read most of them as well. Scorpio Illusion is my favorite, followed by Bourne Identity. I read one of his latest, which is actually written by another author using outlines he set forth before he died. It was decent, but not quite the same.
BTW, stay away from The Road to Gandolfo series. It's a spoof that is supposed to be the worst things he wrote. They were originally posted under a different pen name, before Ludlum became famous.