Benacerraf and Putnam's Philosophy of Mathematics: Selected Readings is a pretty standard (as these things go) collection of seminal papers in the philosophy of mathematics generally, and in the philosophy of set theory in particular (Part IV). Looking farther afield, you could use Maddy as a guide to the literature and go through some of this syllabus, which largely builds around that volume.
You don't say exactly what papers of Maddy's you've read, so maybe this next isn't useful, but I remember getting a lot out of her Naturalism in Mathematics many moons ago, and maybe you'd prefer a single, focused work to a bevy of papers. Rather than a survey, this book takes a particular philosophical stance, and uses it to give a sustained argument against the idea of adopting $V=L$ as a foundational axiom. Along the way, Maddy situates her position among the traditional philosophy of math literature (e.g. Quine), while also dealing substantially with the set-theoretic issues/technicalities that necessarily intertwine with any attempts to do something serious.
Beyond the works already mentioned, if you seek current philosophical work that draws directly on the set-theoretic state-of-the-art, my humble suggestion is to look to folks like Peter Koellner (disclaimer: former advisor) and MO-superstar Joel David Hamkins.
