1. Almost Like a Whale - Steve Jones.
My son handed it to me after he'd read it during his Marine Biology studies.
Basically, it's Charles Darwin's Origin of Species made modern, updated and very readable.
2. Catch 22 - Joseph Heller.
Brilliant book which reminds me of being young, footloose and fancy free...and a lazy summer on Skiathos, and banana beach.
3. The Hitchhiker's Guide to the Galaxy - Douglas Adams
I first read this when I was in my early twenties and finished it in three days. Five years later I read most of it to and with my son (who was about 5 at the time) and found that he had inherited my weird sense of humour. He also says that this got him addicted to reading books.