Sam held the Ring out before Frodo in Cirith Ungol and said he would be willing to share the burden with Frodo, if he'd let him. Instead, in a fit, Frodo snatched it from him. He took it before Sam could quite give it to him. Sam would have resisted the Ring for a long time. But even he, after wearing it, was not immune from the desire of possessing it. Frodo did give up the Ring willingly to Tom Bombadil. Who, after examining it and toying with it, returned it.
Actually, it’s arguable that even Bilbo gave up the Ring when he departed the Shire. But it had laid its claim on him, even though he seldom wore it and had no real notion of its power.
I still think that Sam was the spiritual force behind Frodo’s success in destroying the Ring. He was the unflinching, eternally loyal, none-too-bright but incorruptible conscience that kept Frodo from succumbing entirely to the lure of power. Maybe I give him too much credit but I’ve always thought of him as the salt-of-the-earth Everyman, whose sheer goodness is born of naivete as much as an almost Buddhist lack of Desire.