[Goldberry]

Good thought. I think it was probably sort of a mix of the first two things you said. Probably it was meant to show that even on the brink of destruction, The Ring still had a will of its own; it was resisting its inevitable destruction. Obviously, it wouldn't have been as effective if The Ring had just plopped into the lava and immediately been destroyed. It sitting there for a bit really made that moment seem like a definite climax to the movie. Personally, I really liked the way The Ring slowly sunk into the lava - it showed the evil struggling to preside but the good overcoming in the end.