Patsy Thompson's videos are terrific, but she has many, and I don't know if there is ONE which is the obvious place to start. Her videos tend to concentrate on various designs versus the nuts and bolts of how to begin machine quilting.
Alex's friend, Paula (with the green hair(?) - I'm not sure I remember her last name) has a good video out that covers all the basics. It is very helpful about how to manage the bulk of the quilt, etc.
BethMI