Zeno and the Tortoise [review]
I feel like I need to justify myself for reading this book - it's an introduction to the mental tools of philosophy employed by great thinkers from Plato all the way up to Derrida, and I picked it up not to learn "how to think like a philosopher" (good god) but because it was £0.50 in a second hand bookstore, and Fearn has a particularly lucid prose style. It's a very useful and pithy overview of the history of philosophy, even though it omits a great deal (by design and necessity), so if you're making your first forays into the subject, I recommend it for that purpose alone.