What book would you say changed your life and got you out of a hole (or that helped to get you out)?

I know that reading isn't really a solid replacement for therapy, but I'm just putting it out there. As someone who is currently struggling financially and can't afford a therapist at the moment, I'm looking for something that will at least have a strong impact on me. Something that will just click in my brain and say "Oh. Wait. This is what we were depressed about?" and possibly give me the courage to get myself out of the cycle of negativity.