Kwonkicker (kwonkicker) knows his stuff. He has very clean technique and a technical approach to striking.
Samir Seif (warriorofhonor) is good, as well. He's got experience in lots of martial arts--submission grappling, Wing Chun, Muay Thai, boxing, etc. He was actually on the receiving end of a brutal flash knockout in the WCL if you're interested in seeing him fight. But his technical demonstrations are short, concise, and helpful. He has lots of good videos on padwork and drills.
Damon Faulkner (nopstar) does the Muay Thai Minute videos, and they're very good. They briefly showcase a single technique, such as a kick catch, leg sweep, clinch throw, parry, or what have you. There are also features with some badass nakmuays--Saenchai, Pornsaneh Sitmonchai, Buakaw, Ramon Dekkers, and Kem Sitsonpeenong, as well as others.