A few highlights (I hope Jason doesn't mind me stealing his diamonds)...
Candles and Soap is perhaps my favourite chapter. I'm a fairly strident atheist myself, but I found Jason's take on religion and spirituality very thought-provoking:
The images of religion, from the graven idols all the way up to the One True God--They're all a lot of shadows on the wall of the soul, traceries with which we try to manipulate the things inside of us, the things that science, technology, medication, and therapy can touch but clumsily. Art does a better job than any of these. And religion does it best of all.
That would be spirituality at its best. [...] It would mean burning a candle not to the wax-hungry goddess, but to the ineffable faculty within me that perceives something peaceful, centering, and life-affirming about the ebb and flow of the flame, the impermanence of the wax, and the air of sanctity that generations of experience have pressed into that image. [...] It would mean an answer to the question: Which one of these is going to speak to the part inside of me that could be reached in no other way?
(Reminds me of the Unitarians, come to think of it.)
Curves makes a nice point about how most 'believers' don't really act like they fully believe their dogmas: "if you sincerely believed in the Christian God--I mean, really, sincerely believed in Him--then why would you ever skip out on Church, even once?" It goes on to discuss the (lack of) connection between religious affiliation and personal morality.
Tic Tac Toe is another good one. Not so quotable though - you should just go and read the whole thing. (Even if you don't want to go through the whole novel, this is one chapter that retains its sense even in isolation.)
Chills has one section I particularly liked:
"Philosophy is not the greatest pursuit, but the vainest."
"But philosophers teach people how to think," I replied. "They challenge preconceived notions and help build up knowledge on a sounder, more rational footing."
"Nonsense. Scientists advance human thought; philosophers argue about figments of their own imaginations. Admit it: You too have experienced that guilty rush of pleasure that comes when you consider that the philosopher is the king of all thinkers. It's damn near the only thing that all philosophies agree upon: 'Philosophy is the best.' If shoemakers went prattling about like that, we'd lock them up, and with good reason. Can you imagine anything more transparently self-serving?"
It's funny because it's true. There's also a nice paragraph about socks and intentions, but I've already quoted enough, you can go read that from the original.
Lastly, perhaps the most blatantly philosophical chapter is Imperatives, which contains a wonderful discussion about Kant's categorical imperative. Highly recommended!