I've been using Zamzar.com for a long time to convert files to a readable format.
(Super easy, by the way. If you get a file you can't read, just upload it to Zamzar.com. Tell them the format you want them to convert it to - i.e. a .docx file to a .doc file - and they'll send you an e-mail when the conversion is completed. You click on the link and download your now readable file.)
But, what I didn't know is that you can upload any .pdf file to Zamzar and it will convert the file to .mp3. Yes, the voice is one of those weird robotic voices, but, seriously, this is cool. Let's say your teacher gives you a study guide. (Open Office has a .pdf button in the toolbar that instantly converts it to a .pdf file if it isn't already a .pdf.) You can then have Zamzar convert it to an .mp3 file, sync it to your phone or ipod, and listen. Might be worth a try!!