Some of these are amazing and it's too bad they didn't come to fruition. That Met Life Tower!
I don't know if this counts. The original design for the Dain Rauscher (RBC) building in Minneapolis was never built. I like the original design better than what they built:
Original:
From this great site:
http://www.lileks.com/mpls/dain/2.html
Current:
^that one by me.