I recently started rereading Simone de Beauvoir's Prime of Life, one of her series of autobiographical works. It's thoroughally enjoyable, and though it mostly reads more like a travel biography, her existentialism and feminist philosophy are infused throughout. It's wonderful to hear her talk about Sartre travelling with her almost as an afterthought, because here was a woman who simply loved to travel the world because it was a big part of learning.
It's also a rewarding book for those of us who are approaching 40 and beyond, I think, because Beauvoir used her feminism and her existentialism in the way she saw what growing older is like--the ways in which feminism informs how our roles tend to change (as well as cement themselves) as we grow older and the way in which existentialism can help one appreciate life more as one approaches death. We always choose--that's sort of the existentialist motto, and we're constantly choosing our gender roles as well, even (and especially?) as we grow older.
Beauvoir is a huge influence on my feminist thinking, though strangely not so much directly for The Second Sex. Mostly I think her view of existentialism encourages feminist thought, and not only in the ways that The Second Sex proposes (For me, the Second Sex mainly points out that one is made, not born a woman (or man!).) Her view of existentialism, as somewhat opposed to Sartre's, is that our connectivity to others is fundamental. Whereas philosophers since Descartes have proposed "I think therefore I am," Beauvoir (I'm paraphrasing, of course, and oversimplifying) says something along the lines of "I think, therefore we are." We are fundamentally connected to others existentially; we have language, we are social. And we make choices constantly which inform the choices of others and are at the same time informed by the choices of others. Yes, existence and what it means is ours to choose--we can't avoid that, under her existentialism--but that doesn't mean that the choices are wholly ours to choose. We don't choose in a vacuum; rather, we choose in a social context, among others, influenced (but not caused!) by others, and all the while influencing others along the way.
It seems to me that lots of what feminism can be sprouts from this sort of thinking: the ethics of care, antifoundationalism, theories of social knowledge, and even (though Beauvoir would argue against this) some flavors of postmodernism.
Just some preliminary thoughts. Perhaps I'll have more on Beauvoir and her life (and how it informs my own feminism) later.