do something really mod and graphic maybe? one of my favourite graphic cakes is the one that is top left in this image- http://lotushaus.typepad.com/.a/6a00d8357c6b5b69e200e5529e90ab8833-500wi
it would lend itself really well to a hexagon cake, i think- you could do each side with a different pattern and maybe have the pattern on one or two sides overlap the top edges of the cake. or do a striped cake like this one- http://bluemooncharleston.com/wp-content/uploads/2010/01/striped-cake1.jpg
