You can give reasons or not.
My short list:
René Descartes. "Je pense, donc je suis"
He sure made a fair contribution to science too.
I find Simone de Beauvoir incredibly useful.
The Marquis de Sade worth ruminating on.
Deganawida holds up incredibly still.
Michel Foucault's work is still in need of lots of application and testing.
Friedrich Nietzsche can be terrifying or illuminating, and at his best is probably both.
And, lots of good, meaty philosophy comes down from, or is attributed to, Hillel the Elder and the Younger.
My wife likes Martin Heidegger.
The philosophers I enjoy the most would probably be considered part-time philosophers only; they're often scientists who reached a point in their career where, according to the irreverent words of an old friend of mine, they write books "about God and DNA".
Richard Feynman is probably not a guy who would have referred to himself as a philosopher, but I find more enlightenment in his wide-eyed admiration of the universe's mechanics (made all the more potent because he actually does understand a small bit of it) than in most "real" philosophy works that, in my eyes, often suffer from disconnection from the real world. I mean, I can admire Pascal's Pensées for what they are, but in the end it's clear that the man's got an agenda and that he doesn't need facts to push it forward. Elegant thought constructions are certainly beautiful and worthy of admiration, but even if they say a lot about the human mind, they are at risk of saying little about the rest of the universe -even when that is their avowed purpose.
I did enjoy Montaigne's essays far more than a teenager should have a right to, though.
To attain a happy and tranquil life via ataraxia and aponia sounds like a good plan to me. Way harder that it first may seem, but definitely worth a try.
Leibniz because he had the best wig.
In all seriousness, and to paraphrase Whitehead, the history of western philosophy is really nothing but a series of footnotes to Plato. Plato explored nearly every important aspect of the human condition and, almost always, did a better job than any who came after him.
My favorites are Heraclitus and Democritus. Heraclitus the Obscure is known for his flux doctrine, that you can never enter the same river twice, because the water has changed and you have changed. Heraclitus reportedly died neck deep in manure, in a failed attempt to cure his dropsy (edema), which is a fine metaphor for the pursuit of philosophy. Democritus was known as both the laughing philosopher and the father of modern science. He was very concerned with epistemology (How do you know what you know?) and believed that the earth is round and everything in existence is composed of atoms.
"Injustice anywhere is a threat to justice everywhere."
Martin Luther King Jr., Letter from Birmingham Jail, April 16, 1963
Friedrich Nietzsche is inspiringly strange. I appreciate his work.
Somebody once asked could I spare some change for gas
I need to get myself away from this place
I said yep what a concept
I could use a little fuel myself
And we could all use a little change
My big three would be:
There were also several other Greek phlosophers I studied at university, like Pythagoras, that I enjoyed. And from the Romans, there's Lucretius.
I also like Kant. And I like the poetic language of Nietzche. And if Dostoevsky counts (he's in one of my philosophy books), then him, too--especially in THE BROTHERS KARAMOZOV.
I wrote a bit about Ludwig Wittgenstein on my blog yesterday--
OTF 03.09.13 (my favourite funnies--on the fly)
--where I give a very brief overview of some of his early history--but I don't go into his later philosophical work, i.e. PHILOSOPHICAL INVESTIGATIONS. But he's worth looking at.
I like bits from several, but there are few if any that I really get into. I like Nietzsche for his "God is dead" and notion that we create our own moral values, but am wary of his characterizing most people as sheep and he's tainted in my mind - fairly or not - by the Nazis appropriating some of his ideas. I love Socrates dialectics and Aristotles scientific method, but some of their observations of science and the natural world are so laughable looking back now. I like Kants work aesthetically but find it often over-simplistic, etc.
Pull List; seems to be too long to fit in my sig...