I use Kitabe
I am a member of Kitabe and am impressed with them so far. I've listened to Audio books for several years. It is great way to pass the miles and as a truck driver there are plenty of them. What I like about the MP3 format is that nearly all of them (and all of Kitabe's) are unabridged. I own a LOT of books in tape format, but when I found the tapes starting to go bad I started a program to put my own books into MP3. I've been working on it for a couple of years and then discovered Kitabe.
They have a fairly quick turnaround. I get 2 books ata time and average 6 books a month. I could do better, but my schedule makes it hard. I do tranfer my books to my MP3 player (Archos multi-media 20 gig) and return the disk within two days. Hope this helps