AulŽ's creation of the Dwarves. Impatient that no mortals have yet awakened, he makes his own race, and makes them tough and resilient, knowing Morgoth's power is out there and must be resisted. Eru Ilķvatar then intervenes and points out that, because only he can give the "Secret Fire" of true life, all AulŽ has achieved is the same thing Morgoth and Sauron can do - not to make, but only to mock, and the dwarves are just mindless golems doing AulŽ's will. AulŽ repents and tearfully takes up his hammer to destroy the dwarves...only for them to cower in fear, something that did not come from AulŽ's mind, and Eru reveals he took pity on him, as his intentions were good, and by his grace has given the Secret Fire to them so they might live.
Especially touching was AulŽ's reaction when Eru calls him out on creating the dwarves: he emphasizes that he meant no disrespect like Morgoth, and compares himself to a child mimicking the actions of his father; not from mockery, but from a love and respect for his father.
Also worth noting here is the fact that while Dwarves are certainly not portrayed in the best light, most being self-interested neutral types, they are by far the most difficult race for the Dark Powers to corrupt or trick. In fact, of the seven Dwarven kings who are given rings of power by Sauron, only two join him, another three stay out of it, and two are actually helping the Last Alliance, DESPITE the rings having been in their possession for centuries.
Fingon rescuing Maedhros, despite believing that Maedhros had betrayed him.
Elu Thingol's first meeting with Melian. Also, when Morwen begs him to shelter her son and, in response, he picks little Tķrin up and sets him on his knee, unexpectedly taking him as a foster-son.
Ešrendil is not only spared by the Valar, despite breaking a couple pretty big cosmic rules by stepping foot in the Undying Lands, but they grant his prayers to save what is left of the Elves and good men in Beleriand because they are touched by just how deeply he cares for both kindreds (and this DESPITE the fact that the sons of FŽanor had just kidnapped his sons and tried to kill his wife).
The whole situation is also one for Ulmo, who introduced the loophole into the protections around the Undying Lands that the greatest of mariners could pass through them, knowing full well that one day someone would care enough to come beg the Valar for help.