It can be difficult to take complex ideas and make them accessible, but in Plato and a Platypus Walk into a Bar Cathcart and Klein walk the reader through a first year philosophy course using an easy-breezy style and lots of humor. Okay, the humor isn't that funny (most of it is pretty groan-worthy, in fact), but it does serve to reinforce their basic thesis: philosophy may be a bit nutty, but it shouldn't be intimidating. Anyone can understand the basics---in fact, if you have a sense of humor, you already understand the most important concepts.
I'm always a little skeptical whether these types of books are better as a primer or as a refresher course, but Plato is an easy (and comprehensive) enough read that I'd recommend it to anyone who was interested in philosophy but had no idea where to begin.
Cathcart, Thomas, and Klein, Daniel. Plato and a Platypus Walk Into a Bar: Understanding Philosophy Through Jokes. New York: Abrams Image, 2007.