I've seen some pretty decent to the pretty god awful subway musical performances during my time in New York, but the best I've ever seen, again, can only be described as "pretty decent." Honestly, the most impressive thing I saw on a subway was this busker doing a tonally perfect mimicry of the subway train "door closing" sound. I've certainly never seen anything quite like the performance given by this R&B acapella group, Naturally 7, on the Paris Metro. This group sang their own mixed up (but in a good way) version of Phil Collins's "In the Air Tonight." It's quite stun-tastic. Check it out here. It's funny to note the passengers slowly warming up to them and to see their reactions.