There are a variety of methods to warming up before a grueling workout.  Warming up before a workout routine is a great way to help you get the most out of your workouts.  It can also help to prevent injury.  There are two options to warming up that will push you to working out at your best in very little time.
Warm up Option #1
Start out by jump roping for a minute.
Drop and do 25 pushups
Running in place for one minute.
Drop and do 25 crunches
Jumping Jacks for one minute.
25 Squats
Run the circumference of the room.
Warm up #2
Run around the room for one lap
10 Pushups
Run around the room for one lap
10 crunches
Run around the room for one lap
10 squats
Run around the room for one lap
10 Dive Bombers
Run around the room for one lap
10 v-ups
Run around the room for one lap
10 front kicks per leg
Run around the room for one lap
10 vertical pushups
Run around the room for one lap
10 in and outs
Run around the room for one lap
25 calf raises
Repeat the process for 5 minutes and stretch.
By the end of the workout, you should be perspiring and warmed up enough to stretch properly.  If you want, you can repeat this process for an even more intense warm up.