The four-part story arc that comprises Destination Moon and Explorers on the Moon, because of its complex plot and all the action and danger, especially when it's revealed just what Professor Calculus can do.
In "The Blue Lotus", three giant brute cops get sent into Tintin's jail cell to "teach him a lesson". One panel later we see the three cops in hospital beds, severely injured.
Captain Haddock chasing off the parasites in Red Rackham's Treasure by announcing he feels his ancestor's spirit being channelled through him.
The Crab With The Golden Claws: Captain Haddock charging the Bedouin, screaming vengeance for his shattered whiskey bottle as the Bedouin flee. (Yes, it was because the cavalry was coming in behind, but he was willing to run up to men with guns, insulting them all the while.)
All of Tintin in Tibet, really. Tintin's determination to find Tchang and Haddock's incredible loyalty.
Haddock's reaction to finding out about the slave smuggling in The Red Sea Sharks. His list of insults towards the bad guys never seems to end.
In a non-action example, Bianca Castafiore slamming the doors of Marlinspike Hall in Jolyion Wagg's face in The Castafiore Emerald is an extremely satisfying and long-overdue moment.
Castafiore gets another one in The Calculus Affair where her ability to improvise saves Tintin and Haddock from capture and provides them with the means to defeat the Big Bad and escape Borduria.
The story about how King Ottokar of Syldavia gave his sceptre its mythical status by beating off a violent would-be usurper with it; it helps that his Bond One-Liner from the incident ("If you gather thistles, expect prickles") became the Syldavian national motto.
From the animated series
In "The Crab With The Golden Claws", Tintin manages to get the plane trying to kill him, Snowy, and Captain Haddock to land. He sneaks up behind the pilot, and this happens:
Tintin managing to steal the keys from one of the sailors as the sailors start to pile up due to both the ship moving and Tintin and Snowy hitting the bunks.
The shoot-out at the Karaboudjan, with Tintin avoiding all the sailors while Haddock manages to knock out a couple of sailors and lowers two boats - which helps Tintin, Haddock and Snowy when the ship sailors make a mistake and think the empty one is where they are.
Haddock willingly obliging to the random Mook's (who's holding Haddock at gunpoint, no less!) to raise his hands. He does so... only to send the mook plummeting to the bottom of the ocean.
The hydroplane flight. Special bonus for Haddock vanquishing his fears and using his breath to provide enough alcohol for the plane to reach land.
The ship-to-ship fight between the Unicorn and Red Rackham's ship. Francis de Hadoque's efforts really did a great part in keeping back the pirates, and later when he manages to blow up the ship as he fights against Red Rackham.
The sidecar persecution, with Tintin, Haddock and Snowy fighting for the parchment pieces against Sakharine and his minions. It is a pity that they don't manage to keep the pieces in the end.
Being done in motion capture certainly made it easier, but the fact remains that this is an extremely complicated car chase/parkour scene that is all done in one take. ONE TAKE.
Haddock managing to get Tintin to stop thinking negatively, telling him how his personal experiences shaped him. It also gives Tintin a Eureka Moment, which leads to them finding the Karaboudjan.
The fight between Captain Haddock and Sakharine, as they attempt to finish what their ancestors Francis de Hadoque and Red Rackham started hundreds of years before, starting with the crane-to-crane fight, practically destroying both cranes, and then the sword fight. Tintin manages to save the parchments just in time, and Haddock ends up using the whiskey bottles he finds to knock Sakharine out and finally kicks off his alcoholism.
Haddock: "Thundering typhoons... nobody takes my ship." (next shot has Sakharine flying off the ship into the ocean, then Haddock kicks his last bottle of whiskey off the deck onto his head).
The opening to the chase in Dar Es Salaam has Haddock being surrounded by soldiers. Most people think that Tintin is going to save him somehow, but no. The good captain floors ALL of them by himself. Even with his bad luck and often poor judgement, the man is a Bad Ass.
Hergé's Creator Cameo at the beginning, in which the old and new faces of Tintin are revealed simultaneously.
Tintin: Bad news Captain. We've only got one bullet.