I started taking Crossfit classes about 6 months ago and I am definitely in the best shape that I've been in a long time. Plus, I actually have shoulder and arm muscles! Crossfit workouts are known for being constantly varied and very intense, thus also relatively short. Including warm up and instruction, classes are rarely over and hour. The actual workout can be anywhere from a few minutes to half hour. You can go on the website to see if there is a Crossfit affiliate near you.
We did the "Filthy Fifty" workout last week and really liked it because it worked just about every muscle. I modified the workout so that you can do it at your gym or even at home with little equipment. Just use a ledge or chair for the box jumps and water bottles for dumbbells. Click on the links for videos of each move.
Filthy Fifty (modified from Crossfit):
50 box jumps
50 kettle bell swings (1 pood, or 15-20 lb. dumbbell)
walking lunge, 50 steps
50 sit ups
50 push press (10 lb. dumbbells)
50 back extensions
Do 50 of each exercise one after another. Take limited breaks and have water on hand. Time yourself during the workout and use this time as a benchmark to improve on in the future.