In the books, Saruman forges a Ring and wears it along with a shimmering cloak. This is known when Saruman reveals it to Gandalf. As the title implies, how powerful is this Ring ?
It must be noted that Saruman is no stranger to forging. He served the Valar Aulë the Smith (whom Sauron also previously served). Hence he would have considerable expertise in making stuff. He also studied a lot about Sauron and the One Ring.
Putting all these together, how powerful is Saruman's Ring?