We get lots of questions at the end of the semesters and before midterm breaks about audiobooks, when our students are getting ready to travel home and want something to listen to en route. As a research library, we just don't have many.
I'm going to set up a web guide on free online audiobooks so I'll have somewhere to direct these users rather than just saying "Sorry." I don't know why this didn't occur to me sooner: I have been collecting audiobook links since I got my iPod last summer.
Some stuff I'd include: Podiobooks.com (optional donations), Simply Audiobooks (has some free content), AudiobooksForFree.com and LibriVox (public domain). Fiction podcasts like Cory Doctorow's Craphound; Pseudopod and Escape Pod. Archive.org's audiobooks section.
I haven't really started searching yet, and probably won't get the chance to really work on it until after my vacation. Any good sites I don't know about? I'll add them to this post.