DDR was hugely popular here in Vancouver a couple of summers ago. There were tournaments, classes, and several (popular) websites about it. I got hooked on it, and would spend probably about $5-$10/day, depending on how much I had left from my job, just playing it. Great workout, great music, and fun game =)
I don't play it as much now, but it's still fun when I do. Good songs for a workout (mostly from older mixes) are -
Paranoia *
Afronova
Dropout s4r
and any of the Max songs... very very fast stuff