As the best single and broadest-ranging Catholic apologetics work, I would recommend Prof. Peter Kreeft’s Handbook of Christian Apologetics, available on Amazon and B&N. Prof. Kreeft is a Philosophy Professor at Boston College. If you go to his website,
www.peterkreeft.com, he has a lot of articles on basic philosophical topics, plus a whole bunch of audio files of lectures in MP3 format you can download for free (also available on iTunes as podcasts)
Also anything by F.J. Sheed, particularly “Theology for Beginners” and “Theology and Sanity”, both classics if you haven’t read them yet.
For a basic grounding in philosophy from a Catholic perspective, I don’t think you can do better than Jacques Maritain’s “An Introduction to Philosophy” From the description on Amazon:
Jacques Maritain’s An Introduction to Philosophy was first published in 1931. Since then, this book has stood the test of time as a clear guide to what philosophy is and how to philosophize. Inspired by the Thomistic Revival called for by Leo XIII, Maritain relies heavily on Aristotle and St. Thomas Aquinas to shape a philosophy that, far from sectarian theology in disguise, is driven by reason and engages the modern world. Re-released as part of the Sheed & Ward Classic series, An Introduction to Philosophy is sure to enliven the minds of students and general readers for years to come.
From the new introduction by Ralph McInerny:
You are about to read a magnificent introduction not only to a kind of philosophy but to philosophizing itself. Jacques Maritain was a relatively young man when he wrote this book, but his effort is one that attracts any philosopher more and more as he grows older. However odd and unusual what he says becomes, the philosopher yearns to show how even the most abstruse claims can be put into relation with what the reader already knows. That, in its essence, is what teaching is. In this book, the reader will find a wise and certain guide into philosophizing as such. And, in the end, he will find that what he reads is really only a refinement and development of what he and everybody else already knew.
Professor Feser’s book, referenced above, is also highly recommended, as well as his introduction to Aquinas. G.K. Chesterton also wrote a very insightful guide to Aquinas, usually available bound together with Chesterton’s book on St. Francis.