Hi I've got two suggestions
1) Aussie Aerobics DVD - its got 6 different workouts on it, Aerobics, Bellydancing, Salsa, Fitball, Yoga and Pilates, they are as hard as you want them to be and because there is a variety you can do something different everytime, I thought I would just do Yoga and Pilates all the time (sitting on the floor as much as poss! Ha! Ha!) but love the bellydancing, Yoga and Aerobics the best although I have found a new toy, thanks to fellow minimims!......
2) Podrunner - this is a revelation to me, it is a learn to run beginner to 5k training plan on your mP3/ipod, and it only takes 9 weeks, 3 sessions a week for 30 mins a go on average. I'm a size 18 I have always hated running with a passion (boobs - thats all Im saying!) but I have found myself completely motivated with this, I am on week 6, I've not missed a session and I managed to run for 20 mins non stop the other day, I struggled to jog for 1 minute 6 weeks ago, best of all this is free to download too!! its on Itunes and also if you google Podrunner it will come up, give it a go I cannot believe the difference and progress in me!!! Come on you can do it!!!