Lisa,
I have Yoga Journal level 1 and 2 (Natasha Rizopolous is the instructor) which I have used for several years. I like it because both workouts are just 20 minutes so it is easy to add on to a cardio workout. They are both easy for beginners to follow but still challenging enough. Very relaxing as well.
I have tried some of the Shiva Rea ones with mixed feelings. I did feel that they came closest to mimicking a yoga class. Also the Yoga Journal one I have has very basic poses and it is nice to mix it up. There are a bunch of Shiva Rea dvds and I know one of them I loved but cannot remember the name. A few have felt too "woo woo" for me. You can rent them off Netflix, so that is a great way to try them (I am pretty sure Yoga Journal was available through Netflix too).
Lastly, I like Rodney Yee. I have AM Yoga For Your Week which has 5 20 minute workouts that focus on different things (hips openers, etc). He does a great job explaining things, explaining how your body should feel in each pose.
Hope you can find something you enjoy!