Walking's good too! Anything that gets your heart rate up -- it just takes longer walking than it does sprinting haha.

Have you considered weight lifting? That's my favorite form of exercise to be honest but I haven't done a lot since my free weights got stolen. Your leg would arguably only be partially limiting -- you could probably still do dead lifts and hang cleans and etc. (though I'd be totally wary of squats), and traditional free weight stuff is a great way to exercise without a lot of need for hard movement, just exerted reptition.