When you stop and think about it, it was kind of crazy of Tolkien to make Frodo change his mind about the ring at the very last second. It sure does make for a good read and for a suspenseful finale, but really? after all he had been through? after resisting the power of the ring for so long he end up pulling an Isildur right at the end? It's definitely the right choice by Tolkien, showing that no one is immune to corruption, not even the purest of hearts but man, That took some courage to make that decisions. Most authors would have just have Frodo say something like "For the Shire" before he heroically throws the ring into the fire.
I wonder what would have happened if Gollum wasn't there and Frodo still decided to keep the ring. Would we had a Sam vs Frodo fight where Sam ends up biting Frodo's finger off and then spitting the ring into the fire in glorious slow motion?