consistency, baby, consistency.
that's the key IMHO.
besides that, intensity is important, whatever tape you do make sure to push yourself hard within your own comfort range.
the reason I say 'do what you like' is because the only way to keep a routine is by doing workouts you like. no matter how well-recommended something is, if there is no fun and motivation there for you, ya ain't gonna do it. Just my $.02 cents.
Oh, edited, to actually answer your question
:
Kathy Smith, Kathy Smith, Kathy Smith. Just about any. For cardio, Peak Fat Burning and Timesaver Cardio Fat Burner. For weights, the 'secrets to a great body' series, and "Timesaver Lift Weights..."
I love Kathy Smith, and I thank goodness I found her tapes and was persistent in my early video workouts to keep going. I rarely pull out my Kathy's now, I favor others because my workouts are regularly more intense now than they used to be, but you can bet I've collected many of them on DVD because I consider them CLASSICS that I will always return to.