Sugru's rubbery texture once it's cured and it's moldability when fresh out of the package lends itself well to stamp-making. I played around with several different methods of making stamps with this material and was quite happy with the results.
Sugru: The Most Handy DIY Tool You've Probably Never Heard Of
The miraculous moldable glue known as Sugru is perfect for everything from repairing busted iPhone cables to improving kitchen appliances, and even making the most of any small space by attaching hooks to almost any surface
Casting Objects in Sugru (Make Your Own Candle-wax and Metal LEGO Minifigs!)