R.M.
My fave is, "Pilates During Pregnancy with Niece Pecenka". - She's had 3 kids so she knows what she's talking about and the workout is broken up into two pieces - Abs and breath work: 15 min. and Legs and lower body: 21 min. So the overall workout isn't long, but it's worthwhile. The lower body is crazy good. Meaning you may have better legs while you're pregnant than otherwise!
Hope this helps. I bought my copy on half.com. Just a suggestion.