Hmmm... the best book.... Well there's always the classics, so I am going to stay clear of them and go with a newer book.
"A Walk in the Woods" by Bill Bryson. Tells the tale of an American coming back home after 20 years living in Britain.
Very funny and insightful. Also by the same author "In a Sunburned Country" Read it if just for the opening paragraph!
"All I ask of you is one thing: please don't be cynical. I hate cynicism -- it's my least favorite quality and it doesn't lead anywhere. Nobody in life gets exactly what they thought they were going to get. But if you work really hard and you're kind, amazing things will happen."
Conan O'Brien