Everytime George Bailey delivers a Shut Up, Hannibal! to Mr. Potter (including the very first time, when he was still a kid). Mr. Potter always starts out being all smug and trying to break George (and some others) with his words, deconstructing George's motives for fighting him and losing every time.
As horrifying as it ended up being, Clarence's plan to make it as if George was never born is pretty cool. It starts out as a moment where it looks like it'll be nigh impossible to complete his task and earn his wings, and then he manages to pull it off by using George's own words against him.
Harry Bailey really earned that Congressional Medal of Honor, saving a ship from kamikaze pilots.
Sam Wainwright cables that his office is instructed to wire George up to $25,000 if he asks for it. Adjust that for inflation, today that'd be a third of a million dollars! No strings attached, no contracts to be signed, Sam trusts that George will use it wisely and pay it back.
A bit humbler, but no less awesome for the other residents of Bedford Falls. Not everyone is as affluent as Sam Wainwright- lots of the people donating at the end are the people who've been struggling to pay their mortgages and get through the week, but still scrape together enough money to get George out of trouble because they know he would do it for them, no questions asked.
Best part? Uncle Billy didn't remember it on his own. He talked to someone at the bank, who confirmed that Potter deposited $8,000 right after he'd left. The name of that bank clerk, the person who set the gears turning for some well-deserved Laser-Guided Karma - and cheers from the viewing audience? Why, his name was Clarence.