It's hard for me to answer this question as my philosophical interests boil down to two distinct areas: political philosophy and theology.
In political philosophy I need to say that my number 1 pick would be Leo Strauss - I definitely don't agree with everything he writes but he gets me to think very hard. Next I'd probably say Montesquieu, and finally I'd say the whole kit and kaboodle of 17th century natural lawyers (ie Grotius, Pufendorf, and Selden). Giuseppe Mazinni also gets an honorary mention - to the extent that what he says can be classified as philosophical.
Theologically, Maimonides is the beating heart of my religious thought. However, I do incline somewhat towards a philosophical mysticism, and as such I am very into Moses Hayim Luzzatto's many writings. I find Proclus to be very enlightening as well, and Pico della Mirandola is one of my favorite Christian authors.
I should also add that with regards to political virtue, Plutarch's Lives was the probably the single greatest influence on me throughout my teenage years.