Here's a challenge that I encourage anyone, and everyone, to try: Jillian Michaels' 30 Day Shred. This workout DVD consists of 3 levels in increasing intensity, each approximately 30 minutes long and claims that you can lose up to 20 lbs in 30 days!
I have personally done this workout challenge for the full 30 days on multiple occasions and had lost between 10-20lbs (my results were best when I was actively concentrating on my eating habits, and eating healthy). Each of these routines will make you drip sweat.
As with any fitness routine, you will get optimal results when on a healthy diet consisting of fresh fruits and vegetables, whole grains, and lean protein; limit your consumption of packaged and processed foods to a minimum, or even better, cut them out all together. Fitness is not just about exercise it's about balance between exercise and a healthy diet. Roughly 50% of your results come from your diet; you could workout every day of the week but still not see any results if you're eating junk most of the time.
Trust me, this challenge works; for a minimal cost and 30 minutes/day, why not give it a shot?