We've signed a lot of world class players, but yeah very few who had already established themselves as world class before we signed them.
I'd probably go Litmanen. (Morientes was a big name but probably not quite world class. Ditto Marcus Babbel, good though he was.)
Suarez, Torres, Kenny D, Barnes and a few more were all probably already world class when we signed them, but maybe hadn't yet fully proved it.