I'm a longtime fan of Audible, an audiobook-download service that lets you burn your own CDs and/or transfer books to portable devices (iPods, BlackBerrys, etc.).
The company has offered various free trials and promotions over the years, but this is the best one I've seen: Sign up for a 30-day trial of AudibleListener Gold and get two free audiobooks.
So here's how it works: You sign up for a new account (which does require a credit card), then download the Audible software (available for Windows and Mac, or as an iTunes add-on if you're doing the iPod/iPhone thing). You'll automatically receive two credits in your account, which you can use to download the books of your choice.
After the 30-day trial expires, you'll start getting billed $14.95 per month for your Gold membership, which entitles you to one audio credit, 30 percent off any additional purchases, and a free subscription to The New York Times or Wall Street Journal (the audio versions, natch).
If you routinely buy one audiobook every month, the Gold plan is pretty solid. For example, Jonathan Tropper's "This Is Where I Leave You" (a terrific read, by the way) costs $23.95 on iTunes. If you used your Audible credit, it'd effectively cost you $14.95. Already burned through your credit? Your membership price is $19.59--still cheaper than iTunes.
Of course, you can always cancel your account before the end of the trial, end up paying nothing, and walk away with your two free books.
But if you spend a lot of time in the car, on the train, or even on the biking/hiking/jogging trail, nothing beats a good book. Like I said, I'm a longtime Audible fan. It's a great resource for scoring audiobooks for less than you'd pay elsewhere.