A Random Walk Down Wall Street by Burton Malkiel heavily informed my attitude to investment/savings and put to bed any dreams I had of magically day-trading my way to wealth in my spare time.
Thinking, Fast and Slow by Daniel Kahneman is just generally a really interesting book and impacted the way I view decision-making.
The Wind-Up Bird Chronicle by Haruki Murakami really opened my eyes to unconventional plotlines and surrealist/magic realist themes, and in doing so greatly impacted my exploration and enjoyment of literature and other art.