A tray made of silicone that can be used to make Lego shaped ice cubes.
And it only costs 7.99.
I found this nifty little item on freshfodder.wordpress.com
You can buy your own Lego Ice cub tray from Lego's online store
Imagain creating an entire town or city or castle out of an unlimited supply of lego ice cube blocks, you could even use food colering to color the blocks any color you want. That would be an interesting project. I will post pictures if I ever get around to it.
Wiki article on Ice_sculpture