When still in print, Henri Grenier's manual of Thomism was widely used in seminaries and universities. Those discovering this work for the first time have described it as "the answer key" to St. Thomas Aquinas. Because of the importance of Thomistic philosophy, Grenier's multi-volume manual is being brought back into print. This is a re-print edition of the first edition set, so there are three volumes Volume Logic and Philosophy of Nature Volume Metaphysics Volume Moral Philosophy
Really enjoyed his treatment of the Origin of Man at the end. Even though I'm not sure if I agree with him, his argument for evolution from certain first principles is well done. The state of the question is presented here in a way that is far more productive than the debate over design.
No single philosophy book has been more helpful for me. It might require prior reading, but I think most people could push through. He gives countless examples to illustrate points which were extremely helpful.