Which book has taught you the most valuable life lessons? What did it teach you and how has it influenced your life?
If I have to pick one, maybe Life Strategies by Phillip McGraw, more known as “Dr Phil”, is it. In it he describes ten laws of life. One is you can’t change what you don’t admit. Another is people does what works. If we want them to change, we have to make what used to work not work anymore.
Understanding that people treat me and everyone else in a way that works for them, has helped me many times. If they behave in a way I don’t like, I have to behave in another way than I used to. When they see that their behavior no longer has the desired outcome, they will change their behavior to something else that works for them.
A book I haven't read yet but I wanting to buy is 'Lagom: The Swedish Art of Balanced Living' by Linnea Dunne. I think it will not only be a great souvenir for when I complete my studies here in Sweden, but a great way to learn some life lessons. Has anyone else read this book?
Hm, I would have to say: Living Well With Pain & Illness by Vidyamala Burch . While the book may not be for everyone since it is written for people with chronic pain, it has helped me a lot with my migraine condition. It helped me separate my pain from the act of suffering. 
You have to read this book in Swedish because I don't think you can get it in another language:
Lilian Ryds första uppmärksammade bok var Kvinnor i väglöst land (1995).
About the author:
http://www.norrbottensforfattare.se/indexForfattare.php?xnr=484f984d3eec8&rubrik=2
It is the best book I have ever read. It teaches us about what we lost especially the kids of today.