I am currently in a similar situation. I am way out of shape, and I need to change it.
One of the things I've been doing lately is schooling my horses on the lead. I want them to be respectful and to lead right next to me. So I practice walking and trotting, and even do pivots, backs and setting up. (I even do this with some of the other horses in my barn.) Anything to get your heart rate up. If you have access to a swimming pool, that's great for cardio. Added benefit: it's easy on the joints.
For flexibility and muscle tone, I'd recommend yoga. It improves your balance, flexibility, and muscle tone. An added benefit for yoga is the improvement in your breathing and ability to relax.
Another thing I'm doing for cardio is helping my son practice baseball. Just playing catch and chasing all those stray ones (he's got control issues, LOL) burns a lot of calories. Walking the dog is also an excellent way to go. (I have an overweight doberman, and her weight is NOT controllable by her diet alone.) I'm sure I'll be able to think of more in the morning when my eyes don't feel like sandpaper. ;)
I'm interested in what other people recommend, too.
Learning never stops