Categorizing all the different ways to use poly clay, I had thought to put push molds and rubber stamping the clay into the 'everything else' category, but in my research on sculpture, I decided they could kinda go in this category as well.
A push mold is a mold that has been made from a sculpted object, usually in a bas relief. Poly clay (or other mold-able material) is put into the mold to take the shape of what was molded. After molding, the resulting piece can be used in numerous ways, the face of a doll, on a pin or pendant, as one part of a larger piece, or just the molded piece itself.
We can buy molds, from simple molds, to incredibly intricate molds, to even a whole fairy mold. Or we can make our own molds, usually with a silicone molding material, or even with more poly clay.
There are many FAQ's and tutorials available on the interwebs that can get you started. Push molds can be a great way to make a sculptured piece, especially for a beginner or someone who doesn't care for sculpting by hand.
Rubber stamping on clay makes patterns or textures on the clay, which is a simple way to make intricate looking medallions or other jewelry. There are many places to get rubber stamps, some are more specific to texturing clay, but any and all rubber stamps work. And again, we can make the stamps ourselves, from carving (here's a couple tutorials: One and Two) or having your own art work made into a stamp. When looking for or making stamps, remember to think a little differently than if you wanted the stamps for stamping on paper, the stamping surface will push into the clay, so remember to use that to your advantage.
Both of these methods create a wonderful textured and 3D effect, and have many possibilities, the only drawback that I see, is that if you use a purchased push mold or rubbger stamp, it is not your own handiwork. That's perfectly fine, and a good choice for a lot of people, but if you are wanting to sell what you are making, you'll need to look into the legality of selling something made with someone else's molds or stamps. I learned that there are Angel Companies out there who allow you to use their push molds and/or rubber stamps to make things you are going to sell, so that could be a good option.
I have always wondered how other techniques, especially millefiori and mokume-gane would work put into a push mold or rubber stamped. I haven't seen others doing it, so I may have to try that myself!