Okay, I'll bite. I have time to kill and I love pointing out how cool minor characters are.
1) 'GreatJon' Umber: Everything about The Greatjon is great, starting with his introduction.
And when Lord Umber, who was called the Greatjon by his men and stood as tall as Hodor and twice as wide, threatened to take his forces home if he was placed behind the Hornwoods or the Cerwyns in the order of march, Robb told him he was welcome to do so. “And when we are done with the Lannisters,” he promised, scratching Grey Wind behind the ear, “we will march back north, root you out of your keep, and hang you for an oathbreaker.” Cursing, the Greatjon flung a flagon of ale into the fire and bellowed that Robb was so green he must piss grass. When Hallis Mollen moved to restrain him, he knocked him to the floor, kicked over a table, and unsheathed the biggest, ugliest greatsword that Bran had ever seen. All along the benches, his sons and brothers and sworn swords leapt to their feet, grabbing for their steel.
Yet Robb only said a quiet word, and in a snarl and the blink of an eye Lord Umber was on his back, his sword spinning on the floor three feet away and his hand dripping blood where Grey Wind had bitten off two fingers. “My lord father taught me that it was death to bare steel against your liege lord,” Robb said, “but doubtless you only meant to cut my meat.” Bran’s bowels went to water as the Greatjon struggled to rise, sucking at the red stumps of fingers... but then, astonishingly, the huge man laughed. “Your meat,” he roared, “is bloody tough. “
And somehow after that the Greatjon became Robb’s right hand, his staunchest champion, loudly telling all and sundry that the boy lord was a Stark after all, and they’d damn well better bend their knees if they didn’t fancy having them chewed off.
And then he really does become Robb's right hand. Any important move Robb made, The Greatjon was in the thick of it. He then gives the Kingindanorf speech, easily solidifying his place on any top five list.
The Red Wedding was a tragedy, with many horrible deaths. Among those fell the Smalljon in a true feat of courage. But the Greatjon lives, and the North Remembers.
Sorry, I was having too much fun with that one.
2) Ser Arthur Dayne: The Sword of the Morning. I have talked before about how I love how Martin takes a seemingly low fantasy environment and infuses various elements of high fantasy in varying levels of potency. Arthur Dayne is one of those pure high fantasy bombshells, that Martin is able to use by hiding him a decade and a half in the past.
He is the only knight I would say rivals Brienne of Tarth for the title of Truest Knight in Westeros. He is a prevelant part of the Tower of Joy, what I consider another one of Martin's high fantasy jackpots.
During the reign of Aerys II, the smallfolk of the Kingswood's lives were so shitty they would house the fugitives of the Kingswood Brotherhood because they looked so poorly upon the crown. Arthur Dayne, with his kindness and generosity alone, were able to win over the smallfolk and had them stop one of the things giving the Brotherhood a major advantage.
He then defeats the Smiling Knight in single combat. The Smiling Knight is referred to as the Mountain of his day, not because of his size, but because of his lunacy, brutality, and how formidable that made him in combat. Not only does Dayne win the fight, but when his opponent's sword is worn down during combat, Arthur pauses and allows him to get another, following it up with one of the best lines of the series.
The outlaw’s longsword had so many notches by the end that Ser Arthur had stopped to let him fetch a new one. “It’s that white sword of yours I want,” the robber knight told him as they resumed, though he was bleeding from a dozen wounds by then. “Then you shall have it, ser,” the Sword of the Morning replied, and made an end of it.