What about BodyRock?
It can be very high impact, or it can be no impact- but it will kick your butt. She always shows modifications for all levels. The workouts are intense, but only last 12 minutes a day. Doable by anyone's standards. I get my arse kicked every time I do it (although I wish I could motivate myself to do it every day).

Is your fear of the water something that you think you could gradually get past? If you hired a swim coach and got a little instruction, could you possibly consider getting in the water?? When I've been injured and couldn't run, I would water run for an hour in the pool (boring as heck, but it mimicks running and is a good workout). Or you could use a kickboard and kick (fabulous leg workout). Both of those wouldn't involve putting your head underwater and would give you control. Just a thought.

And riding, of course! There's always riding.