My first organized cardio routine was Couch to 5K. I can’t recommend this program highly enough. I went from having difficulty running for more then a few minutes to three 30 minute runs in the final week. Read all of my posts on Couch to 5K here.
Currently, my cardio consists entirely of swimming but I’ll eventually give that up. Now that the weather has warmed up I’m planning on getting back to running with the idea of participating in more races.