Mixing it up is generally best. Gillian already gave some great ideas, one other thought is to set up an STS style rotation with the dvds you have. So for one month do the more endurance/high rep stuff, second month do heavier but more traditional weight workouts (full body and/or splits), then in the third month do heavy weight/low rep workouts. There are not many high weight / low rep dvds that I know of though other than meso 3 in STS and the weight work in 4 day split, so that may take some adjustments to other dvds or doing workouts without dvds.