Libro.fm is a neat alternative to Audible. Points in its favor: DRM-free; kick-backs to independent bookstores (I chose Toronto's awesome Flying Books); credits never expire; not owned by Bezos.
Like with Audible, the first month is free. Switching from Audible? First three credits are free by using the code SWITCH. Yes, they have far fewer books than Audible, but the selection is pretty good overall and the sale books have some great titles.