If you are looking for a Shia ring either already made or custom check out Shia Rings.
I've found the quality of the stone and workmanship of the silver to be excellent. If your going to request a custom ring be sure to give exact instruction, whether the top of the stone should be flat vs. rounded, whether you want Arabic writing on the stone etc.
It is sunnat-e-muakkedah (very commendable) for men and women to wear a ring on the right hand.
Here is a nice video you can watch to understand the wisdom behind stones and why the Ahlulbayt place much emphasis on certain stones in rings.