Nonmachinable mail can be all sorts of shapes as well. I've had a lot of fun cutting cardstock into silhouettes and irregular polygons and mailing them.
When I moved, I sent postcards notifying people of my new address in the shape of my new state. US mail is quite flexible thanks to the nonmachinable surcharge.
Yes I should have mentioned that. If you want to send any weird shape or a piece of wood or something (I recently sent some postcards I'd cut from raw veneer/scrap from a sawmill) the no-machine/hand-cancel fee is the ticket.
