Groupon offers an Audible 2-Month Trial Membership for free. That's a savings of $30 and tied with our mention from two weeks ago as the best deal we could find, outside of the mention below. This trial gives you a free audiobook download for each month.
Note: Promotional value expires 90 days after purchase. Be sure to cancel your membership before the trial ends to avoid a recurring $14.95 monthly charge.
Also, Amazon also offers it free for Prime members.