Okay, here's a new theory concerning Saruman and Grima.
Saruman, who was a Maia of Aule just as Sauron once was, became learned in Ring-lore as he studied Sauron's evil works. Too well learned, as it turned out; for Saruman gradually turned to evil himself, emulating Sauron's works. Saruman also experimented with the making of a Ring of his own. Here's part of Gandalf's account to the Council of Elrond (Fellowship of the Ring, pp. 271-2 hardback, italics mine):
"'...and there he [Saruman] met me and led me up to his high chamber. He wore a ring on his finger...But if Saruman were to experiment with making Rings of Power, he wouldn't make only one, would he? No; I think he'd make at least one other, and try to get his ring to exert an influence over the wearer of the other. And who would he give such a ring to?
"'..."For I am Saruman the Wise, Saruman Ring-maker, Saruman of Many Colours!"'"
Grima Wormtongue seems the obvious answer, since he was so completely under Saruman's control.
...Kind of helps you see Saruman in a new light, doesn't it? Sure, Sauron may have had the Nazgul, the Ringwraiths; but perhaps Saruman in his turn had Grima, the Ringworm! :)