There are lot of good "workout" type DVD's - some of Bert Kinister's, Joe Tucker, Bob Henning, or Pro Skills Drills. They all focus on certain key shots that come up frequently and work on your ability to make the ball and get to the center of the table, or up to the end rail, etc.
I also like the PAT series, good combination of knowledge, shot making and position drills with a nice way to score, also progressive so as you get better you increase distances or add balls to add to the difficulty. The level 3 drills are tough!
Scott