Metal rubber band guns from Japan.  Looks pretty cool.  It’s probably cheaper and easier to make a lego rubber band guns though, but they obviously wouldn’t look or be as cool.

http://gigazine.net/index.php?/news/comments/20100207_wf2010_w_kerberos/

http://gigazine.net/index.php?/news/comments/20090726_wf2009_s_silverwolf/