I came across this interesting site this morning:

LibriVox volunteers record chapters of books in the public domain, and then we release the audio files back onto the net (podcast and catalog). Our objective is to make all books in the public domain available, for free, in audio format on the internet. We are a totally volunteer, open source, free content, public domain project.

Here is a little more detail about how it works:

1) LibriVox volunteers suggest books from the public domain, and we’ll choose some to record.
2) Volunteers “claim” chapters, and record them to mp3.
3) Volunteers get the files to us, somehow!
4) We host our files on the wonderful Internet Archive
5) We maintain a catalog of complete and incomplete books, and podcast selected books

They need volunteers so if that is something you want to get behind head over and check it out. Of course, if you just want to listen head over for that.