I like the Pregnancy Fitness dvd set from Target by Lindsay Brin - it is a strength/cardio combo and has a different dvd for each trimester, as well as a post-baby bootcamp. She's a bit too cheerful at times, but I don't mind too much.

I have a prenatal yoga dvd also from target (can't remember the name at the moment) and it's pretty good too.

The Summer Sanders' dvd is growing on me, too, but it's not my favorite.

I like Summer Sanders' prenatal workout. Pretty athletic, especially good for ladies who used to lift before getting pregnant. Has specific workouts for each trimester.