The Whac-A-Mole game from Episode 40, the Dream Card episode. Sakura was struggling to hit all the moles coming from all around her, so Meiling decided to grab a hammer and help her out. With each other's backs covered, they had the time of their lives smashing up moles. Especially awesome is that Meiling used to hate Sakura with a passion and constantly distrust her when they first met, but at that moment, they were playing together like they've been best friends forever.
Against the Twin Card, Syaoran and Meiling's perfectly synchronized attack was the greatest display of Badass Normal in the whole series.
The second greatest being Meiling vs the Fight Card.
Meiling during the episode when Sakura is forced to transform The Freeze; not only does Meiling manage to stop a good deal of the large stone/metal penguins with just her bare hands to protect both herself and Sakura, but it's her idea to use The Freeze in the first place. Later, her very selfless and very immediate I Want My Beloved to Be Happy moment, a huge leap from the Clingy Jealous Girl that hated Sakura that she once was.
Tomoyo using her singing prowess to help capture the The Song card is a unique case. She similarly does this to help convert The Song into a Sakura card later on.
Also, how Sakura caught The Jump. Specially because at some point the girl (who mind you, was still a Na´ve Newcomer and basically realising how the deal worked) summons The Fly while taking a huge fall and being upside down. A little mistake and she would've died, but she managed to get this perfectly done.
With the risk of applauding assault against a minor, The entire Final Judgment. Poor animation aside it was one of the most brutally actioned scenes in the anime.
A meta example: NISAmerica managed to rescue it. They're giving it the full blu-ray remastered treatment. Best of all, they're using the Animax dub, which, according to Madman Entertainment, is supposedly EXTREMELY taxing and hard to get (even though it's in mono only). That takes massive balls and guts to do. They must really love this show if they managed to give it this much royal treatment.
Syaoran's mystical entrance at the very end shot of Episode 7. From now on, the series will not be the same...
In the anime, Syaoran serves as a more Worthy Opponent to Sakura, earning a dozen or so cards himself prior to the Final Judgement. Seeing him use some of the cards effectively is likely gratifying to his fans from the original manga. Sakura sometimes sucks the sport out of it by outright letting him have the card however, in which case it becomes a Heartwarming Moment.
Syaoran has a recurring tendency for pulling acts that are noted shouldn't be possible with his magic level. Yue notes his surprise he managed to overpower both Maze and Illusion in Episode 66. Punctuated since these are nearly always to protect Sakura.
Sakura defeating Eriol's final test, bringing sunlight to Tomeda so everyone will awaken from their otherwise permanent slumber, and converting all of her remaining cards in the process. Bonus points for Kero and Yue taking form inside her wand to empower her.
Syaoran, despite being affected by the spell, manages to stay awake throughout the entire thing, despite weakening himself to save Sakura from an attack and helping her with the load of her final spell. Oh, and he finally spits it out.
The fight against the sentient railing in Episode 61 is one of the more intense tests in the final arc. Extra props because it's the nearest Syaoran gets to actually using his sword properly, with Sakura's staff working just as effectively.
The opening to the 2nd movie with Sakura slicing through a earth monster with Sword, Keroberos fending off a fire monster, and Yue calmly destroying yet another one is made of sheer win with the music on top of it adding the feel. Then it turns into a Crowning Moment of Funny when it is revealed it's actually a video and performance staged by Tomoyo.