There's something that I've wondered about for some time. At the Council of Elrond, no one, not even Gandalf, suggests that the Eagles be recruited to fly the Fellowship, first to Gondor, and then, after a period of practice and training, to Mount Doom. The Council occurs during an opportune window in the story, since at that time, the Eagles had already proven their capability to transport passengers (e.g., Gandalf's air rescue from Orthanc), and Sauron has not yet had time to re-outfit the Nazgul with airborne fell beasts. They could fly the Company from Rivendell to a suitable location in Gondor, then take some time to probe Mordor's air defenses. At this point, Sauron, is probably still focussing on places farther to the North and West to find the Ring and its carriers. Once it's established that the Eye of Barad-dur is not directed due west, Frodo and some of his companions can be flown to the Sammath Naur before the Ring has had time to cause him enough spiritual corrosion for him to want to keep it.