Which is the most stunning lens for a Canon camera?

I want to amend my list, having just gotten a Leica R 135/28 in the mail.

This lens is as good or better than my R 60/2.8 macro (in every way but macro ).

I'm just stunned by how good some lenses can be. I know not everyone will agree, but here is a lens that proves the point that great equipment can make a better photographer.