For a programmer on vacation, I wouldn't recommend a technical book. Go for something that will exercise the right side of your brain, the parts that don't get as much work day-to-day. Your left-brain is what you're trying to rest and refresh; that's why you're on vacation after all. I'd go for something on the far end of the spectrum; some forgotten modern classic that won't let your left-brain to kick in, like Return of the Native. If you absolutely must have something technical, the aforementioned Neal Stephenson books are great, as are William Gibson books. The Little Schemer is a good book to go through while you're NOT on vacation.
Also recommended in this reply