EnCapture Artisan Concrete allows you to embed glass, gemstones, metal, buttons, wire, beads and more. It's great for creating custom jewelry pendants, mosaic work and more. You can mold it into shapes, dye it, paint it, carve it, stamp it, etc.
Envirotex Jewelry Clay is another great craft medium. Easy to mix, shape, mold, and texture, Jewelry Clay provides excellent adhesion to stones, crystals, glass, metal, wood, and more. It provides a smooth porcelain like surface that will not shrink when cured.
Swarovski Ceralun was especially developed for use with crystals, and works great for embedding small baubles in jewelry and craft designs. It works best on surfaces of glass, metal, gluable plastic, rubber, wood, cork, and porcelain. Get Swarovski Ceralun while you can - Swarovski has exited the DIY market.