As I've said before in my review of Jillian Michael's 30 Day Shred I'm kind of obsessed with this woman.
Out of the multiple Jillian DVD's I own this is the most used and loved. Don't let the title fool you though - it works WAY more than just your abs! A lot of her moves involve the butt and thighs and there is a significant amount of ab work done in plank so your shoulders get a fantastic workout as well.
While you can do the workout without any weights I would suggest you have at least a 3 to 5 pound weight on hand to do some of the moves as your core strengthens. The DVD is broken down into two 30 minute workouts (level 1 and level 2). Each workout starts out with a brief warm-up then a full circuit of varying ab moves. After the first circuit you go through all the moves again but in double time. Level 2 is much harder than level 1 and it took me about a month to be able to complete it without feeling like someone stabbed me in the kidney the next day.
If I can get the courage up to actually show off my abs one day I can illustrate how effective this workout has been for me. I will do it 2-3 times a week in addition to core work in my other workouts like pilates or circuit training. While I don't have the stellar 6 pack like Jillian does I have noticed my waist shrinking and my lower abs particularly strengthened (You know, the dreaded lower belly kangaroo pouch).
One tip for this dvd: sometimes I like it best when used in combo with another activity and only going through the first circuit of the level. For example, I try to work out for 45 minutes a day so one day I may start with her Ripped in 30 DVD then follow it up with just 15 minutes of ab work from this DVD.
As with all my reviews if you have any questions about the workout or would like recommendations for similar DVD's please ask! After trying enough crappy home workout DVD's I love being able to share those that are effective and easy to accomplish with very limited equipment.