I know there are some golf fitness books/DVDs out there, but I can't think of any off-hand.
I do yoga regularly, and as you might expect, it's a great exercise for stretching. What surprised me however, was how much strength I gained as well. Terrific exercise.
Do you live in the U.K. ? If so, join Fitness First and do their "Fit for Golf" workout. You can join for 30 quid a month or so. Worth doing.
__________________ "Golf takes us away from our everyday worries. It allows us to lose ourselves in the beauty of our natural surroundings. And it provides a serene setting for enjoying the camaraderie of our fellow players. No matter how good we get at it, golf always makes us strive to do better. In golf, as in life, there is no perfection, but we can always seek it. Golf constantly challenges us to aim farther, try harder, and be more than we are today. And really, what game could be better than that...?"
I dont have a book to recommend either. Everything Ive read and heard is all about the stretching. Being more flexible only leads to more control and more swing speed with less effort. The other big one that adds the power is doing any kind of exercise for lats. I have a bowflex and I do pull downs and a few other exercises for my back, shoulders and chest. Upper body strength and being flexible while toned is what gives you distance. And of course having more strength and endurrance will always help you finish a round strong and be more in control of the club. Not the greatest advice in the wrodl but its all I know and its helped me a little.
To stress the importance of stretching, I used to have a swing speed around 110mph with a driver and now Im down to 98mph because I've put on all this extra muscle in the upper body w/out maintaining my flexbility. So you could say Im a moron for not keeping up with being flexible anymore because after putting on 10 pounds of muscle I swing slower.