I have just found a Yogazone one called 'Postures for pregnancy'

Even though I'm not yet pregnant, I've started to do it, so that I can continue it easily when I am. It's really good, they also help to teach you how to open up your rib cage so that in later pregnancy when you're big, you're less likely to be short of breath. It is very easy and basic, but still gives a good work out. Another thing I liked about it, is that at one stage, the pregnant demonstrator wobbled and fell over a little, but they didn't edit it out, they left it in, which made me feel it's a very honest production LOL.