I've done yoga on and off for the last 3 years (I'm off now b/c of a knee injury), and think it's absolutely the best for stretching my muscles and relaxing my mind. I go to a weekly class and when I leave, I feel both relaxed and energized, if that makes sense . . .

I do traditional hatha yoga (the emphasis is on breathing and standard poses), so although I sometimes feel sore in a few of my muscles after a session, it's not really a muscle builder for me. Perhaps "power yoga" may do more of this? I haven't used any DVDs, though, so can't recommend any. For me, yoga is perhaps more important as a mental break than as exercise. Have fun, whatever you decide to do.