The best way to exercise with your baby is to get a well-made stroller and get out walking! It's a wonderful way to get a cardiovascular workout, and babies love getting look at all the exciting things going on out in the world. I'm not a big fan of including babies in strength training (i.e. using the baby as a weight -- you already lift her hundreds of times a day and you really can't focus on your form when your more focused on holding your baby). I do like to have moms lay their baby next to them while they do stretches on the floor. Babies get a kick out of seeing mom do all those movements and even try to imitation some times.