Project Gutenberg is a website that puts expired copyright books on the internet. Which is fine, if you like reading stuff on a computer, or want to pay more to print the book out than it would cost to just buy it in the first place.
But I have found something else that they are doing: turing these books into audio books. Now if you want an audio book for a trip, just download the chapters and burn them onto CD. Viola, (almost) instant trip entertainment.
Now that is really useful.