The Hitchhikers Guide to the Galaxy. It's the first in a trilogy of six books. I haven't read the last book but I would recommend reading 1 to 5.

The radio series and audiobooks are all worth a listen as well. There is a version narrated by Douglas Adams himself and another narrated by Stephen Fry and Martin Freeman. Both are great.

One of my favourite quotes from the Hitchhikers:

“You know,” said Arthur, “it’s at times like this, when I’m trapped in a Vogon airlock with a man from Betelgeuse, and about to die of asphyxiation in deep space that I really wish I’d listened to what my mother told me when I was young.” “Why, what did she tell you?” “I don’t know, I didn’t listen.”

I also love this quote from the fourth instalment of the series So Long, and Thanks for All the Fish:

The storm had now definitely abated, and what thunder there was now grumbled over more distant hills, like a man saying “And another thing…” twenty minutes after admitting he’s lost the argument.

The whole series is worth a read. You're bound to laugh over and over reading them.