Who saved Middle-Earth?  

Gollum. Frodo was going to keep the ring for himself when he jumped on him and bit his finger off. XD

But he wouldn't have done that if Frodo and Sam wouldn't have first gotten the Ring that far. So I think Gollum should be added to the credit-geters. Although, unlike Frodo and Sam, he never MEANT to save Middle-Earth. Which is why I never give him credit for his part in the end. :D

They both did, in their own way, but Frodo definitely deserved the most credit. And even though he gave in to the power of the ring at the end, I believe he would have overcome it with Sam's help.