When I'm pregnant I feel limited as to what kind of workout I can get in, especially once my bump starts getting in the way. Two of my favorite basic ways to exercise are swimming (obviously) and walking. Both activities keep things low impact and fun. Jumping in the pool to do some basic stretching or yoga gives almost instant relief from the extra weight and discomfort of my growing belly while walking works out the aches and pains in my hips and lower back. Lucky for me if I get lazy I have Blaise (my son) who reminds me it's time to play in the pool and three dogs who remind me to take them out for a jaunt now and then.
Tip: Keep it simple and don't over do it. Always check with your doctor first to make sure the intensity and duration of your exercise routine is right for you and your growing baby.