It’s not free, but very affordable, and such a great teacher resource or self-study tool. I somehow missed talking about this core addition to your teaching resources. And if you’re studying American English pronunciation on your own, this just might be the best thing you’ll find.
This 6-CD + study book set is designed to be used by students as a self-help tool, but it’s perfect for teachers as well. Cook not only “covers all the bases” of American pronunciation, she also provides easy-to-understand nationality guides, in which she lists the major interference points for speakers of other languages. The only thing lacking is a feedback loop for those studying on your own—you’ll need a way to know if you’re making the correct pronunciation adjustments or not. You’ll have to provide that yourself, but that’s not difficult really. If you have a native-speaker conversation partner, ask them for feedback. Or download something free like Audacity from sourceforge.net and record yourself, listen, re-record, compare yourself to the audio models on the CDs, etc.
If you’re teaching pronunciation for the first time, or you’re frustrated because you are unable to help your students improve their pronunciation, invest in this set–you won’t regret it. I’ve been teaching American pronunciation for years, and Ann Cook’s kit is still one of the first resources I grab when I want to refresh my memory about the problems Arabic speakers have, for example, or the problems I can expect with my Chinese clients.