Pilates and Yoga have both become quite "trendy" in the past several years. My health club offers Power Yoga in a heated room as well as Pilates, no machines, just floor excercises.
I love how Pilates defines my body. Yoga is also good if you do an equally intense workout.
It really is personal preference as some people swear by Pilates and some swear by Yoga. If you want a good Yoga experience, check out Mark Blanchard's Progressive Power Yoga. He is a celebrity trainer who will whip you into shape!