I don’t recall how I came across Rachel’s English but I was instantly impressed and have yet to explore its entire depth.
The first thing I found was the list of sounds represented by the phonetic alphabet. There is also a sound chart that lists every sound a letter can represent. Both of these have links to YouTube videos like the one above, which detail how to pronounce the sound. I especially like the portion of the video that compares pictures of Rachel in profile as she pronounces the sounds with her teeth, tongue, and other relevant anatomical features drawn over top (for example, see the 3:50 mark in the above video.) These photos are also available in the mouth positions section. There are also other interesting exercises and a blog.
In addition to being a useful pronunciation resource, a lot of attention is paid to linking everything from various sections appropriately. It doesn’t matter if you are looking through the sound chart or pictures of mouth positions; you can always link to the relevant YouTube video for a quick 5-10 minute tutorial on a given sound.
This is a useful site for students to work through on their own. Perhaps more importantly it could be something teachers recommend to students to supplement classroom instruction. If students are having trouble articulating a particular sound, email them a link to the video, then suggest they follow up with one of the exercises. Working through some of these clear and informative tutorials might be just the extra help they need.