Thinkgeek sells a set of silicone D20 ice-molds for $12. I've never had good luck with two-part molds, but that product-shot is pretty spectacular, and the documentation makes reference to an ingenious-sounding interlock system that has you freezing the bottom half of the mold, locking the top on, filling it up and refreezing. If that works for you, you can also get a Death Star ice-mold.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.