Reddit reviews Ideal Voice and Speech Training

I have a great little book called "Ideal Voice and Speech Training" by Ken Parkin, that I cannot recommend enough. It's full of excercises of Monophthongs, diphthongs, triphthongs etc., and has a lengthy section of tongue twisters and other challenging passages, such as Major General, and The Chaos. There's also a list of Shakespeare speeches for various moods and emotions.

I should also recommend the work of the late and vastly talented voice artist Vivian Stanshall, who wrote and performed Sir Henry at Rawlinson End. If you know the album, or even if you don't, you can practice with this transcription of the complete piece, which features many different-voiced characters and is presented episodically.