I Am a Strange Loop by Douglas Hofstadter - strongly influenced my beliefs about how consciousness works
Godel, Escher, Bach by Douglas Hofstadter - made me think more deeply about so many topics
Animal Liberation by Peter Singer - made me both an animal advocacy activist and strongly influenced me towards a consequentialist moral
Neuropath by R. Scott Bakker - more on how consciousness works, this time through a work of fiction
The Dispossessed by Ursula K. LeGuin - strongly influenced my beliefs about political systems
The Selfish Gene by Richard Dawkins - changed how I thought about animal behavior and what living things do
Republic, Lost by Lawrence Lessig - strongly influenced my beliefs about US government
Manufacturing Consent by Herman & Chomsky - made me rethink my view of the media and news