In addition to many of the already-mentioned titles, I took a lot away from:
The Power of Positive Thinking
How to Talk to Anyone, by Leil Lowndes - super practical
Alan Watts, The Book - On the Taboo Against Knowing Who You Are - (easily the most influential book I read on Eastern philosophy)
The Brain that Changes Itself, by Norman Doidge - incredible understanding of how we can change our own neural pathways
Everything written by ethicist Peter Singer, including The Ethics of What We Eat (I'm not a vegan, but his arguments are excellent)
Everything written by Michel Foucault, if you are interested in ideas of power and knowledge/ poststructuralist/postmodernist theory and metaphors for societal institutions
There's also an excellent book capturing debate between Foucault and Noam Chomsky about human nature
The Brighter Side of Human Nature: Altruism & Empathy in Everyday Life - by Alfie Kohn (ps, if you have kids, Alfie Kohn's other works have guided my parenting style significantly: Unconditional Parenting: Moving from Rewards and Punishments to Love and Reason and Punished by Rewards: The Trouble with Gold Stars...)
Animal, Vegetable, Miracle by Barbara Kingsolver
I also really like David Brooks works, including Bobos in Paradise, On Paradise Drive, and the Social Animal. All are excellent reflections on American culture, written with intelligence and humor. I re-read Bobos every time I need to reign in irrational spending on "practical" things and want a laugh.
Also, my husband and I have both really enjoyed reading John Gottman's works. Otherwise known as the only scientific study of marriage books out there. The Science of Trust was more meaty (in terms of outlining the research process) than some of his previous work, but we have read all of his books.
Finally, I just read The Other End of the Leash by animal behaviorlist Dr. Patricia McConnell, and it seriously changed the way I interact with dogs! Ha! So "changed my dog life".
We, by Yergeny Zamyatin (the lesser known predecessor to a Brave New World/1984/distopian novels)
The Phantom Tollbooth, by Norton Juster - just excellent wordplay at its best and opens up creativity
The End of the Affair, by Graham Greene was just an excellent book covering raw human emotion