Black-and-yellow Garden Spider, Argiope aurantia.
I photographed this big, beautiful female yesterday. The appearance of these orbweavers and their large webs is a sure sign that summer is waning. Black-and-yellow garden spiders will be with us until the first killing frosts of fall. The male was nearby; he is but a fraction of the female's size and must tread cautiously when approaching her to mate. Garden spider are harmless enough to us, though, and valuable cogs in the food chain. It's best to just leave them be.