Amtrak's snowflake maker is pretty cute--simulating cutting a snowflake out of paper. Needs Flash, I think. What appears to be exactly the same snowflake maker is also available at Popular Front. (I think PF created it for Amtrak.) Here's my snowflake (have to wait for it to load, and then to "fall" (labeled "your friend's"); may take a while; may not be worth the wait).
Barkley Interactive has a similar snowflake maker, though the interface isn't quite as nice.
At Evil Mad Scientist Laboratories, you can create a snowflake using a little application written in the amazing Processing graphics language; you can output it into various vector graphics formats formats, and then if you have access to a "CNC machine, laser cutter, 3D fabber, vinyl cutter, or so forth," you can create a physical copy in vinyl, metal, or other material.
At Zefrank, the snowflake drawing tools are more limited, but you can rotate the result in 3D.