Scientists have been fascinated by snowflakes since the invention of the microscope. The most realistic simulated snowflakes to date come from mathematicians David Griffeath and Janko Gravner. Their most recent work on the subject generates elaborate three-dimensional "snowfakes" down to the microscopic ice caves inside.
For an explanation of their snowfakes and some realistic images, see the slideshow at Discovery. There are more architectural-looking drawings like the one above in the math paper: Modeling snow crystal growth: a three-dimensional mesoscopic approach