If you like the idea of making your own molds, there are materials sold specifically for that purpose. Many polymer clay artists make their own molds from polymer clay, too. Regular clay makes rigid molds; flexible clay (Sculpey Super Flex by itself of mixed with Premo) makes flexible molds. Either works wonderfully well at capturing details from your favorite beads, buttons, jewelry findings, leaves, or whatever else strikes your fancy.
Certain items around the house can also be used as push molds-anything that doesn't have an undercut. For instance, a measuring spoon or the round indentations in a painter's palette can be used to make cabochons.