Another online audio chat site... Does not seem to offer private discussions, so may not be too useful in the classroom. (I have not created an account to confirm this, but there is nothing on the site to suggest privacy settings.)
Forvo is the largest pronunciation guide in the world. Ever wondered how a word is pronounced? Ask for that word or name, and another user will pronounce it for you. You can also help others recording your pronunciations in your own language.