I started running 4 weeks ago and I sprained my ankle. I hate exercise and am worried that this will derail my progress. While I haven't seen great weight losses yet, I am excited about exercise for the first time and I have actually substituted walks/runs for cookies.
All athletes get sidelined! A sprained ankle can take a long time to heal and the risk of re-injury is high. I hope you have see your doctor for the proper treatment and rehabilitation. A health professional can give you a rehabilitation program to improve your balance and strengthen your ankles and legs. But in the meantime, until you heal, the best cardio exercises for you are those that don't put pressure on the ankles. Swimming, water aerobics, rowing, bike riding, Pilates, yoga, and tai chi come to mind. Read more about ankle sprains and ankle sprain rehabilitation at About.com.