I'm often impressed that top mathematicians in a given field seem to have not only a knowledge of the "state of the art" of their subfield, but also a knowledge of the history of the field and thus the seminal books/papers in the field.
In this direction, I would love to have a list of classic math texts (books, especially) that rate today not as mere historical curiosities, but that would be of benefit to a graduate student to read as a first introduction to a given field. Thus in some sense I'm asking for classic books that have not been rivaled or replaced. Are there such books? I'm told that Weyl's The Classical Groups is such a book. Are there others?