I won the Marta Montenegro Method 3 DVD set from Brooklyn Fit Chick, check out her blog HERE. I am particularly fond of the Strength and Endurance dvds, each of which contains three workouts. The workouts are about 20-25 minutes long, which makes them easy to fit in during a busy day. They are tough! The first time I did the first of the Strength workouts, my glutes were so sore I was feeling it for four days! You will need a light pair of free weights for this workout (I've been using five pound weights). The first Strength workout focuses on arms, the second on legs, and the third on core. I would compare the Strength dvd to Jillian Michael's Shred, only more challenging. Also, I have to admit that I like Marta's calm, matter of fact persona better than Michael's in-your-face attitude. The Endurance dvd workouts are also extremely challenging - they will get your heart rate up within seconds of getting started. I particularly like that they involve plyometrics (movements of jumping expulsion) which help build speed in runners.
If you are looking to get a maximum workout all-round value for your time, you can go purchase the Montenegro Method HERE. It's definitely a worth-while workout for these long winter days.