I'll second the videos by Mark MacYoung as well as those by Hock.
Mark's videos are very good for basic knife defense, but that does not mean they will only benefit beginners. I've seen too many advanced martial artists get "too advanced" with their training that they forget the basics.
Hock's videos are very good for practical training and are full of drills. TM 1-3 (the basic package) has more material than some arts at blackbelt level.
I'll also add "Gunsite Tactical Edged Weapons" by Rich Ryan, it is basic but good for using folders which is what most of us actually carry.
I also like the DeCuerdes Eskrima video Richard Van Donk sells, taken from a seminar by Grandmaster Tenio.