If you're looking for a great way to get in shape fast (and probably the toughest workout you've ever done), look no further than the Tabata Protocol. It's a form of high intensity interval training (HIIT). If you are already training very intensely in the weight room with high volume, I wouldn't recommend incorporating Tabata intervals into your workouts. However if you're trying to lose weight, get in killer shape, or are taking it easy on the weights, go ahead and try this workout a couple times a week. Trust me, you won't need to do anymore.
The process is simple: go as hard as you can for 20 seconds, rest for 10 seconds, and repeat 8 times for a total of 4 minutes. The best exercises for these are sprints, jumping rope, kettlebell or dumbbell swings, kettlebell or DB snatches, KB or DB cleans, or any bodyweight exercise (push-ups, squats, etc.). This is one of the best fat loss workouts out there. Tabata training is also nice during the winter, when it can be hard to train outside. They're also great when you're short on time and much more fun than running on the treadmill. Also, they're great for basketball players (or other athletes) because they're easier on the knees.
Here is a couple articles on Tabata training: