I really struggled with trying to figure how to break into this competitive field. After years of banging my head against the wall, I came across a great site called acx.com.
This site is a great resource for aspiring narrators. You simply create a profile (for free!) and start auditioning. It's really that simple. Publishers listen to your auditions and decide if they want to hire you.
Now, the one caveat is that you are responsible for fully producing a finished audiobook, so if you aren't adept at recording AND editing, be careful not to commit to something you can't complete. Editing is not my strong suit, but I'm fortunate to have a good friend and business partner, Jason Noxon who is not only a gifted voice actor, but also a terrific audio engineer. I couldn't have completed the two audiobooks we've recorded so far without his expertise.
If you need help producing the book, there are great resources on the site to link you up with studio professionals who can help you. Just be aware that there's more...much more... to the process than just auditioning.
So go check out the site and start auditioning. Let me know how you make out!
UPDATE: My second audiobook is now available on amazon.com, audible.com and itunes!! Here's the link to the audible.com site. Please check it out!