"The Second Sex" by Simone De Beauvoir is on here twice. I'd recommend if you're looking to read an existentialist book by the same author - check out "The Ethics of Ambiguity" which is an attempt to form an existentialist ethics, and is short, and good. Tbqh "The Second Sex" is a bit dry for modern tastes - even though it is important. I'd recommend reading something like Judith Butler's "Gender Trouble" if you want a better feel for modern feminism.