Audiobooks are an important tool for learning a language, and are a source of edutainment.
Librivox is a group dedicated to producing Copyright free, public domain, human read audiobooks out of works in the Public Domain. Their content would serve well on the OLPC.
However: Librivox tends to let Archive.org encode their final work, so it ends up in two bitrates of MP3 and one of Ogg. For most purposes Ogg Vorbis is a great codec, however it is not the best encoding for audiobooks.
So, for Librivox Audiobooks to become part of the OLPC content bundle, they should be encoded in Speex.