I have never been able to find one, but if you leave one computer on at all times, just run orb. It streams video from your home computer to your pocket pc in a format that will play. It also allows you to do youtube searches and have your computer convert it to avi and forward it to your phone. My ppc now replaces my ipod cause I can stream all my music and ripped movies to it.
It the core pocket media player. It's an excellent replacement for pocket windows mobile. The combination of that and orb should set you on your way to watch youtube on your phone.