I recently discovered several superb, low-cost study guides on the classics of philosophy. They are authored by Laurence Houlgate, Ph.D., who is Emeritus Professor of Philosophy
at California Polytechnic State University, San Luis Obispo where he was a beloved colleague and teacher. He wrote the guides after his retirement in order to keep a promise to his former students.
I have read parts of all of the study guides and the voice of a good teacher and scholar can be heard on every page. I highly recommend them. Just click on the picture to be taken to one of the low-cost guides. (Also, Professor Houlgate has a great philosophy blog.)
Finally, let me say that the modern philosophers above are some of my favorite thinkers in the Western tradition. Well worth becoming acquainted with them if you are not already.