Pilates.  There are the modern Pilates movements which are center stage or floor based and really works all of the joint positions (turned in like markial arts, normal like a jazz stance, and turned out like in ballet), the traditional pilates is done on machines and sometimes with a partner to help in elongating, think Allonge'.

Anyway, I do Yoga two times a week during the colder months to keep limber.  I use Yoga to decompress my spine, lengthen my body, and rediscover my core.  That being said, it is helpful in dance.  I have been looking for a Pilates class in my area with one successful location, however I dont agree with the instructors philosophy (which is: "to pack the room").

My private dance instructor has shown me some pilates moves to help with lengthening some of my movements.  My jazz class instructor does nothing with the class for warmup (of course I do on my own).