5 Audible classics are on sale for $0.99 ea until April 29th. If you buy 4 or more of these that should qualify you for the Buy 4, Get $10 promotion and you'll get a $10 coupon to use in May.
The Importance of Being Ernest is still free.
A short story by Bill Pronzini is free.
ETA: Not Audible, but if you are interested in audiobook deals,
Tantor has Thomas Perry's Vanishing Act free this month, and are offering all his audiobooks for $6.99.