Hartshorne's AG, unquestionably. Eisenbud's CA in my opinion (not from the 70s but the 20th century nonetheless), but more uncontroversially Zariski and Samuel's. Also Mumford's Red Book. Milnor and Stasheff's book on characteristic classes. Adams's Blue Book on stable and chromatic homotopy, and Ravenel's Green Book on the same (again, the latter was not around in the 70s but is still from the 20th century). Tbh any book that's commonly referred to by its color is probably a classic.
Oh, and EGA. Obviously.
EDIT: If you count physics (and books from the 80s), Shankar's book on quantum should be on the list. Likewise with Feynman's Lectures in Physics series and Taylor's Classical Mechanics. I would also argue for Purcell's EM text, although people seem to have shifted away from it lately in favor of generic "intro physics" bullshit like Giancoli.