Thanks for all the suggestions, and especially for the advice to check Youtube. I was able to preview quite a few of the DVDs there.
These are the DVDs I ended up ordering from Amazon, as I think they will provide me with a range of workouts from relatively easy to relatively challenging (although the list below is probably in reverse of that order!):
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1