The Complete Muay Thai Home Study Course: Secrets from Thailand.

Bit of a cheesy title but this is an excellent instructional.
4 DVDs covering: Pad work; Muay Thai clinch; Kicks & elbows; Nuts and bolts (tactics).
Shot on location and involving three instructors from 3 gyms (Lanna Muay Thai,True Bee, and Chay Yai Muay Thai).

This is a superb collection of DVDs and it's entertaining as well as having useful lessons. There's a lot to learn here but they keep it interesting. Cost me 100 US dollars and it was well worth it.

There's a clip on Youtube (Muay thai home study course secrets from Thailand) which should give you an idea

Selling for 29 (which includes P&P).