What's your favorite non-mold mold??
Know what I mean? What's your favorite mold that was not intended as a mold, meaning something you found that makes a great mold. My latest favorite is not very original, but it's a 6" length of pvc pipe. Cheap (1.99!) and it makes the most lovely round bars of soap. I thought the burly men at the hardware store were going to give me a hard time about cutting a piece of pipe as a soap mold, but they didn't blink an eye...
Also, I'm loving the icecube trays from IKEA. They are square rubber trays, and I now have the hearts, stars, x's and o's and long bars (good for embedding in a loaf pan). They are so easy to work with because they are flexible and make nice little embeds (or guest soaps).
So, reveal your latest discovery!