Due out in November, (you can preorder it here), SimCity Societies promises to let you build cities anyway you want to. Taking a different approach to previous SImCity incarnations, it's less about planning infrastructure and more about shaping a society.
It looks like it'll feature a fairly sophisticated 3D building editing toolset too.
Perhaps I'll get further with simulating Okhitovich's Red City of the Planet of Communism with this version than with previous versions of SimCity.