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 himnote His ancestor, Sir Francis Haddock, was the man who killed Red Rackham in single combat.
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.
In the Prisoners of the Sun, two men are harassing Zorinno, a small boy selling fruits. Outraged, Tintin rushes up without any hesitation and beats the snot out of the bullies, despite them being bigger than him. When they try to retaliate, they don't even score a single hit and their only resort is to run away!
The protagonists' victory over the Perry in the climactic last stretch of race to the meteorite in "The Shooting Star".
Between 1971 and 1989 Cupol (later acquired by CBS, now Sony Music) published Swedish audio cassettes of the albums, covering each one from Congo to Picaros. While that in itself might not be all that unique the high quality of the productions are. Not only do they each follow the albums as closely as possible, the voice cast is outstanding and they kept the same actors for the recurring roles for nearly every single production (the actors also reprised their roles for the Belvision series). Each cassette is narrated by Tintin, as voiced by Tomas Bolme, and Bolme's performance is considered by many Swedes as the real Tintin. He also manages to narrate events as they unfold and make it work without sounding silly, which is no small feat. Also worth mentioning is Åke Lindström as Captain Haddock, who gives a passionate performance that manages to take the Flowery Insults to a new level. The recordings have later been released on CD and are now available on Spotify (and, in some cases, on YouTube).