Indycar before the second split (from the beginning to 1995)
Nigel Mansell winning the 1993 Championship, which was done despite a back injury he sustained at Phoenix which troubled him throughout the season. He won on his debut in Australia (a country he usually struggled at in F1). He'd never raced on an oval before; and won 4 of them! Adding to the prestigiousness was the fact that he was going up against veterans like Andretti, Fitipaldi, Tracey, Al Unser Jr, etc. He'd never even sat in an Indycar prior to 1993 and still came out on top. He remains the only driver to hold the Formula 1 and Indycar titles simultaneously.
The 2003 Toyota Indy 400. This race is known as the fastest in motorsports history-400 miles completed in just 1 hour, 55 minutes, and 51 seconds. Cautions would normally prevent this series' races from being this fast, but this race only had one (debris from laps 74-79), and the result was winner Sam Hornish Jr.'s average speed of 207.151mph.
CART/Champ Car after the split (1996-2008)
Indy Car after merging with CART(2008 and onwards)
Will Power shedding his "can't do well on an oval" and "can't finish off the season" images with an impressive victory at the 2013 500 mile season finale in Fontana, holding off the previous two 500 mile race winners (Ed Carpenter at Fontana in 2012 and Kanaan at Indy in 2013). While Power was well out of championship contention by this point, winning three of the last five races including Fontana helped salvage enough to get him back to 4th overall in the season.
And the next year, he finally won the series championship...by 62 points over second-place Hélio Castroneves.
In 2016, a year after James Hinchcliffe was nearly impaled to death by his own suspension at Indianapolis, he returns to the Speedway and puts on a thrilling run in the Indy GP, finishing third for Schmidt Peterson's first podium of the season. And then he wins the pole for the 500 itself, which is also Honda's first pole position in the series since 2014!
On a broken right hand and with many questioning if he'd take time off, Josef Newgarden starts dead last at Road America in 2016 and grits his way through the field to finish eighth. Two weeks later at Iowa he thoroughly dominates all day for his first oval victory, at one point putting the entire field except Simon Pagenaud a lap down.
Sebastien Bourdais' passing three cars in one left-right move in turn 1 at Long Beach 2018 jumping from 6th to 2nd in one corner. Then the officials rule that technically one car was passed using the assistance of the pit exit lane (a no-no for obvious safety reasons) so he has to give that place back (to Scott Dixon). It ended up not mattering that much, as Bourdais and Dixon were then so far ahead of the next cars that he could let Dixon past on the back straight...and overtake him (legally this time) again in Turn 1 the very next lap.
1912 - Ralph DePalma pushing his car around the track after the engine failed. This didn't win him the race, but he certainly showed a lot of heart. He'd get a win in 1915.
1985 - the "Spin and Win". On Lap 120, Danny Sullivan moved to attempt to pass race leader Mario Andretti on the inside. Sullivan's car slipped coming off the apron and he went into a 360-degree counterclockwise spin. Amazingly, not only did Sullivan not make contact with anything, but his car ended up pointing the right way and the engine caught when he put it back in gear. After a pit stop for new tires and fuel, Sullivan passed Andretti for good 20 laps later and cruised to victory.
1989 - the final laps, highlighted by the Brazilian coverage. The main commentator, Luciano do Valle, got ecstatic (and hammy) in the moment when Emerson Fittipaldi got inside of Al Unser, Jr. to pass him in the final laps (if you prefer, you can see it in this video)
Luciano do Valle: Look he closing, he is near of Al Unser, take a look, EMERSON GO INSIDE, GO! GO! GO! YOU CAN PASS HIM! NOW ITS BRAZIL! ITS BRAZIL! GO! GO! JUST A LITTLE MORE EMERSON! Take a look AL UNSER CRASHED! AL UNSER CRASHED! AL UNSER CRASHED! EMERSON GONNA WIN! EMERSON GONNA WIN! BRAZIL WON! BRAZIL WON! THATS BECAUSE THE YELLOW FLAG COME AND EMERSON IS THE LEADER! BRAZIL WINS! BRAZIL WINS! (starts to play a victory fanfarre). A-ma-zing, Awesome! This victory is going to be in the history of all of us! Amazing! Brave Emerson put his car inside and didnt allow him to pass!
1992 - Al Unser Jr.'s victory, the closest finish in Indy 500 history. After his heartbreaking defeat in 1989, "Little Al" suddenly found himself in the lead when Michael Andretti's car quit with 11 laps to go. Right on his tail was Scott Goodyear, who had started P33 and in last (due to being substituted for his teammate Mike Groff, who had qualified the car). Goodyear chased Unser for the last 10 laps, then came side-by-side as the checkered flag flew. While the official margin of victory for Unser was 0.043 seconds, most accept that it was even closer because Unser's transponder was in the nose of his car rather than the standard placement in the sidepod.
2013 - Tony Kanaan finally winning, after countless, fruitless attempts.
2015 - Early on, Simona de Silvestro accidentally bumped Juan Pablo Montoya's car, breaking a piece of bodywork off. Montoya's car still ran, but he had to go into the pits to get the rear end replaced. Doing so dropped him down to 30th place. Despite this, he managed to work his way up to first where he was when the checkered flag dropped.
2016 - in the 100th running, Alexander Rossi, former F1 driver and an Indycar rookie, racing for a modest team (Herta with Andretti assistance), wins the race with a risk strategy of saving fuel. This was the first time a rookie won since Hélio Castroneves in 2001.
Winning on a fuel gamble doesn't begin to tell the tale. Rossi's crew botched two stops early in the race, falling to 20th and 25th after those two stops. Herta and Rossi agreed the only way to even come close to winning was to start conserving fuel with ninety laps to go—almost half the distance and about three full stints. Their final stop, forced by a caution, was with 36 laps to go, when most drivers could only stretch a tank to 32 laps at best. It took a remarkable combination of drafting on teammates and non-teammates, engaging the clutch (putting the engine in neutral to save gas by coasting), and running a super lean fuel mixture at race speed-one that's normally reserved for driving under caution-merely to have a chance. Rossi still ran out coming off of turn four to the checkers with just under five seconds to spare, the margin of victory over Carlos Munoz.
And even Castroneves, and Montoya before him in his 2000 victory, were only rookies by definition of making their first appearance at Indianapolis and being required to pass orientation. They already had plenty of seasons racing ovals in CART. The 2016 Indy 500 was Rossi's second oval race in his entire professional career, after racing at Phoenix in April. The next previous rookie to win the 500 was Formula One champion Graham Hill, fifty years prior.
2017 - Takuma Sato fought long and hard to become the first Japanese man-nay, the first Asian-to win. With shades of Al Jr in 1989 and 1992 it was made sweeter by the context of his near-miss in 2012 when he crashed trying to pass Dario Franchitti in Turn 1 for the lead on the last lap. Many fans thought he had been harshly chopped by Franchitti who then won under caution (and likely the fact that Sato was very much the underdog while a Ganassi car won again, and shots of Franchitti's then-wife Ashley Judd celebrating the under-caution win didn't endear the 3-time winner's third victory much either).
2018 - Will Power won, but that's not the impressive part. The impressive part is his colorblindness, and strictly speaking was at a disadvantage his entire career, color being an important part of motorsport.
2019 - Simon Pagenaud winning, becoming the first Frenchman since Gaston Chevrolet, ninety-nine years previous, to do so.
Marco Andretti winning the pole, 33 years after his grandfather Mario last won it.
Takuma Sato became a two-time winner this year, but not before getting involved in an incident on pit road with Alexander Rossi, then having to get around none other than Scott Dixon to do so.
2021 Just when you thought Spider-Man was done... he climbs the catch fence again. Yes, Hélio Castroneves won his fourth 500, tying the all-time record. After being shunted by Penske to its sports car program. After winning the 2020 IMSA series championship, only to see himself let go when Roger Penske decided to entirely shut down Team Penske's sports car program.