For balance work, I really like the Wii. Several years ago I started tripping occasionally when out walking with my husband, and I noticed my ability to recover balance was very poor. Spending about 20 minutes per day on the Wii improved my balance a *lot* over a period of about 6 months. Forgot about it for over a year and am just now starting back on it. My balance is still better than when I started, but have noticed some degradation lately and my Wii scores prove it. It will take me awhile to get back to where I was, but well worth it.
Not sure there is any one thing that will work on muscles, balance, strength and flexibility all-in-one.
I've tried several DVDs for flexibility, etc. but find with all of them that I get too bored. The Wii games keep me more interested.