I think Chicago's "Millenium Bean" is an amazing piece of public art. The reflective nature of it has people coming up and interacting with it, which I think it a hallmark of good public art. But given Chicago's "gangsta" reputation, I'm (thankfully) suprised I haven't seen any pictures of it being tagged.
Anyway, not to rip off Chicago, but I think Seattle needs it's own bright shiny thing (and not a monorail!).