If you are a total beginner, and have never been to a class I recommend:
Yoga Journal's "Step By Step" dvd series. (They have 1, 2, and 3)
Google it...you can buy them on eBay, Amazon, and from Yoga Journal's site.
They are fabulous, because they give much more info on proper form. I would avoid anything by Kathy Smith, Denise Austin, or anything put out by general fitness instructors or celebrities if you are new to yoga. Proper form is important to avoid potential injury.
Start with volume 1, and when you have mastered all of the poses, go on to Volume 2.
I also recommend "Introduction To Yoga" put out by Yoga Zone. It gives nice tips on form as well.
(I am adamant in having yoga dvds by real yogis, not celebrities or step aerobics instructors...)
Also, be sure to have a yoga mat, a yoga strap (or a belt), and 2 yoga blocks for most dvds. The last two things will help you modify positions if you need to.
Start weight after baby #3: 233.9
Current weight: 143
90 pounds lost!