I seem to remember seeing a documentary a while back where they discussed a music video in which they had an attrative standing in for the real singer, lip-synching to her song as the record company deemed the actual artist to be not good-looking enough to appear in the promo. I think it was an '80s or '90s house tune - then again, it wouldn't surprise me to learn this happens (or at least used to happen) a fair bit, especially in the case of one hit wonder dance tracks.

Can anyone think of any particular examples?