Sucks about the wrist, but if you're careful, you can still exercise. Obviously, any bodyweight exercises that don't require the arms are fair game, such as running, sprinting, air squats, pistols, squat jumps, box jumps, lunges, step-ups, and sit-ups. Only real worry is if you slip and start to fall, you need to make sure to only catch your self on the good arm.
Weighted exercises are a bit trickier, but not impossible: depending on what kind of mobility you have with your cast, you can do front squats without actually having to grip the bar. That is, the bar can just sit on your deltoids (see the bottom two images
here) and your hands are only there to slightly proper it up. There was even a video of some Crossfit guy doing back squats with one arm in a sling, though that seems a bit dangerous to me. Besides squats, you can do on armed exercises that are primarily powered via hip/leg drive, such as KB swings, KB snatches and KB cleans. I'd be hesitant of doing too many one armed exercises that use a lot of arm strength (such as one armed pull-ups, push-ups, presses, etc) as your injured arm will already end up weaker due to the injury and training the healthy arm will only make the imbalance greater.