Ballet! Also interesting. And quite a workout, I have to say; not so much while I was doing it, but I certainly felt it in muscle fatigue for much later on - I understand much better now why dancers like pilates. As for benefits in cross-training, I'd rank posture, balance and coordination in the main. One thing I really noticed was that whereas the martial arts I usually train in have conditioned me to find the most effecient way to perform a given movement, in dancing it seems almost the complete opposite, with control and the extra energy put forth to generate grace taking precedence. In the same sense, however, that might be stemming from a very basic understanding of the latter, and now that I think about it perhaps when the basic dance movements are more conditioned the grace comes naturally from within the dancer and/or their mindset. Hmm.