Fundamental videos.

Coach:

Depends on the level you coach. Bill Williams has a lot of tapes you can copy after you join his organization (pricey). One of my long-time favorites is the Mervin Johnson's Oklahoma Offensive Line tape. Also, look at the Bishop Dullaghan tapes. They are good yet inexpensive ($25). There are so many tapes out but not all are good in their fundamentals teaching. To each his own.