The assault on the castle in Shrek The Third, which is fully the princesses' time to shine. Of particular note is the beginning. Snow White hops out and starts singing happily and luring out a bunch of woodland creatures... then her happy trilling turns into the Immigrant Song.
Everyone showing up to back up Shrek on stage during the third one. Including Dragon & her kids flying in formation and the 3 pigs in martial art poses. Yes, Charming ruins it by calling in the villains, but still...
Any scene with Shrek riding Donkey as a Stallion.
The Piper's "Shake Your Groove Thing" sequence in Shrek Forever After. Whatever your opinion of this movie, the Ogres, Shrek, and Fiona dancing to that is Crowning Music of Awesome.
In Shrek 2 the Fairy Godmother orders the King to slip Fiona a love potion so that she'll fall in love with her son, Prince Charming. The King places the potion in Fiona's tea but finds that he can't go through with it, and gives his daughter a cup of tea that wasn't laced with the love potion instead. His response to the Fairy Godmother's outraged "Harold, you were supposed to give her the potion!" is a smug "Well, I guess I gave her the wrong tea."
Fiona's headbutt on Prince Charming after he plants a Forceful Kiss on her.
Prince Charming: "This was supposed to by my happily ever after!"
Shrek: "Well, I guess you'll have to keep looking. (Looks to Fiona) Because I'm not giving up mine."
Artie's speech at the end of The Third, convincing the other villains that, yes they do have a choice. fits well with the series idea of "There is always another ending".
In the third movie, when Artie gets picked on by the students, Donkey of all people (having been stuffed into a locker and having a "I sucketh" note planted on his butt) snaps at them "Ya'll should be ashamed of yourselves!" Defied quickly when Lancelot says "That wasn't me." Still, a funny talking donkey standing up against the bullies is kinda cool.
In the first movie, Fiona interrupts Robin Hood's song with a flying kick to the head, then curb stomps the merry men.
In Shrek Forever After, Fiona gets an off-screen moment of awesome: it's revealed that after waiting so long for a prince to come, she eventually just rescued herself. And then she led a rebellion.