Running/walking is what I have been doing for cardio as well. Doing the Couch to 5k in 12 weeks program but at a slower pace. I have been on week 7 for about 3 weeks now.

I have found though, that fitness walking is much more enjoyable for me than running. The pounding is just too much. I don't feel like I am getting any where. Whereas, fitness walking feels like am just gliding over the ground. I love it! gimme some good music, my doggie and I am gone!