I've been really enjoying the concepts from STS - working muscle groups really hard just once a week, but rotating the muscle groups. Like one week I might do chest and back; biceps, triceps, shoulders; legs. Then the next week change and do back, shoulders; chest, biceps, triceps; legs. That sort of thing.
I've also done a little mixing and matching and have done like one or two muscle groups from a strength DVD (like Gym Style) then add on the same muscle groups from a muscle endurance DVD (like Power Hour).
There are sooo many options! LOL