Buy MP3 Audiobook Player Pro. It's really easy to use, plays mp3's (duh lol) which can be easily dragged & dropped trough itunes (the complete map the book is in), remembers where you paused the book you're listening to, remembers several books (up to 4 I think), can be put on homescreen as widget (just klick and listen)
To put books in the app:
- open iTunes
- select your device (on top of the screen, left)
- on the left, select "apps" (might be called otherwise on new itunes, the bottom one)
- on the right, select the audiobook app
- now drag any folders with books (or music of course) and drop.
On the very top of the screen under the apple logo you will see a line advance. if that's complete klick "ready" on the bottom right.
Open the app and give a few seconds to update library. Select a folder and go