I was recently asked about references for orofacial or tongue exercises for sleep apnea. In my experience, all these exercises work to various degrees. There are a number of resources on the internet that I know of:
Janet Bennet has a DVD/training program for snoring. She’s a speech pathologist that accidentally discovered that exercises for tongue thrust helped with snoring significantly.
This paper showed that orofacial exercises can significantly reduce snoring and symptoms of sleep apnea. There’s even a free short video that shows the various exercises.
A paid exercise program for sleep apnea. A more condensed, free version can be found here.
This is not an oral or tongue exercise, but playing the didgeridoo has been to be found helpful.