I agree with Donna Tartt's "Secret History" and love a couple of the other choices, but seriously, "American Psycho"? That's not even Bret Easton Ellis' best book.
I would lead this list with "Retro Hell." Just saying. And somewhere on there would be "Microserfs," Ariel Schrag's high-school saga (perhaps she's a Millennial?), Melanie Thernstrom's "The Dead Girl," Steve Almond's "Candyfreak," the achingly touching "Somehow Form a Family," and a few others.
What books would make your list, either written by authors born in our generation (be generous, call it 1960s to 1980s) or about it?