I love Sam's song. It's the first one I memorized from LotR, and not just because it's relatively short. “Above all shadows rides the Sun, and Stars forever dwell; I will not say the day is done, not bid the Stars farewell” is a line I've used to keep myself going on rough days for a long time. Not that I've had to go through anything approaching what Sam has, but still.
Sam's time as Ring-bearer is very illuminating. Poor Boromir, with his desire to protect Gondor and his dreams of personal glory, was very vulnerable to the Ring's temptations. Sam is a very different person:
Wild fantasies arose in his mind; and he saw Samwise the Strong, Hero of the Age, striding with a flaming sword across the darkened land, and armies flocking to his call as he marched to the overthrow of Barad-dûr. And then all the clouds rolled away, and the white sun shone, and at his command the vale of Gorgoroth became a garden of flowers and trees and brought forth fruit. He had only to put on the Ring and claim it for his own, and all this could be. In that hour of trial it was the love of his master that helped most to hold him firm; but also deep down in him lived still unconquered his plain hobbit-sense: he knew in the core of his heart that he was not large enough to bear such a burden, even if such visions were not a mere cheat to betray him. The one small garden of a free gardener was all his need and due, not a garden swollen to a realm; his own hands to use, not the hands of others to command.
Sam isn't proof against the Ring - no one is - but the grand ambitions the Ring is made to fulfill are wasted on humble dreams like Sam's. An arsenal of ICBMs isn't so useful if you're looking to win a snowball fight, and Sam is and wants to be a gardener, not a Lord of Gardeners.
The Watchers are another of me favorite things. We don't really have any information on what they are or how they work. They're statues, but there is certainly a mind there, or at the least a will. And with nothing but a will, they nevertheless manage to be menacing and frightening in the extreme.
They are another example of a theme I've mentioned before: the greatest feats in LotR aren't acts of skill with a sword or great feats of strength or Odysseus-like cleverness: they're acts of courage. Sam's defiance of the Watchers was his own bravery, with an assist from Galadriel's light in dark places. Just as Gimli's walking the Paths of the Dead was a great feat, and the slaying of the Witch-king didn't require any particular skill on the part of Éowyn and Merry. It's a theme that goes back to The Hobbit, when Tolkien explicitly says the greatest deed in the story is Bilbo mastering his fear and walking down the tunnel with a dragon waiting on the far side.
Now that Frodo and Sam have finally made it into Mordor (by walking; yes, yes, you're very smart. Now shut up) they find themselves in the Land of Shadow.