I have to recommend "Skills" with Ryan Hughes, I found it on the Transworld Motocross website and I believe it's a lot more up to date than Gary Semics.
Ryan Hughes actually does a great job teaching, who would have thought?
Another video I bought was Jeremy McGrath's "Techniques of a champion" but I'm sorry to say that it's almost a waste of money, no real insider info here, just very basic stuff.
There's a new site online called motocrossguru.com, I would like to join but don't have paypal, that might be an even better learning tool than the DVD's, I'd definitely investigate that one.
Just my 2 cents, Carl