I've been a member of Audible.com for a few years, 45 min commutes are much easier when I can listen to a good book instead of the traffic report.
I only buy unabridged audio books, I don't like missing any of the details that the author/editor/publisher thought were worth printing. You may want to check out the selection and make sure that the genre you are interested in has enough books for you. Since I read/listen to sci fi, fantasy, and romance there are lots of books for me to listen to.
You can download the audiobook with your phone and again on your desktop. I have an iPod so I can listen on my iPod, iPhone and desktop with iTunes, I use to load them onto my Windows Mobile PDA as well. There are other options, the Audible software page
has a wizard to walk you through what software options you will need for your useage.