I planned to do some lifting this evening before teaching Insanity, but ended up a little behind schedule, leaving me only about 15 minutes to fit it in. With 6 exercises, each working multiple muscles, I knocked out 2 sets with heavy weights, followed by a few minutes of plank work. A couple of hours later, and I'm already feeling that work in my body! The key is to have a plan and move quickly between exercises with minimal rest between. Using heavy weights helps burn out the muscles with few repetitions. If I had a little more time, I probably would have done the circuit a third time, and still would have been under 30 minutes for a complete strength workout.
As far as cardio, I've been teaching a 30 minute version of Insanity a couple times per week. Those 30 minutes are super intense and leave me burning calories at a higher rate for hours after I'm done. I've also been using Shaun T's T25 here and there on days when I don't teach or can't make it to the gym. The same rule applies, focus and push through at a high intensity and you get an effective workout in a short time.