Those of you who have read Teaching & Learning Pronunciation would have probably watched Jennifer's video lessons on vowels, although I'm not sure if all of you had realised that there were more videos apart from the one I embedded. You can navigate through the playlist by clicking on the arrows to the left or to the right of the video image.
Jennifer (Thanks, Jenny!) has just published another lesson as part of the series, this time on diphthongs. Before watching this, make sure you have watched the other videos on single vowels.