On OffbeatBride, a great (but complicated) HOWTO for making your own polyhedral chocolate dice molds from your D&D dice, and then cast delicious chocolates from it:
How to make your own Dungeons & Dragons chocolate dice mold (via Neatorama)
Before we begin, some disclaimers. First and foremost: This is about as complicated and expensive (net cost: $100 + shipping) a mold as you're likely to get, for anything reasonably sized. (Well, unless you want molded daleks complete with little plunger-arms or something else that is fundamentally not a convex shape.) That's because it has a lot of little, tiny, fiddly pieces, and it's a two-piece mold meant to create solid 3D shapes with no flat back. And the little fiddly pieces are of variable depth so you need way more silicone than you would if, say, you were just molding your favorite buttons. Chances are, your mold doesn't need to be this insane. But that's fine! You can still use this tutorial, just skip the pieces that are clearly irrelevant.