Some school libraries are starting audiobook collections, an easy (and free) way to do so is with Creative Commons and public domain titles.
Librivox - volunteer-read public domain works
Spoken Alexandria Project - creating audio books of creative commons works
Podiobooks - free serialized audio books
Lit2Go - a free online collection of audio stories and poems
Project Gutenberg - human read public domain audio books
X Minus One - a series of science fiction radio plays, not technically audio books
Cory Doctorow - an author who creative commons licenses his works, a number of them have been recorded as audio books by him or by fans