this is so tough coz my mind keeps bouncing between scenes from The Melancholy of Haruhi Suzumiya, Nichijou, Mekakucity Actors, Lucky Star and Sonic X
like if we're talking melancholy the Narato vs Ryoko fight is one that always stick with me but so is Endless Eight or the last few scenes from The Disappearance of Haruhi Suzumiya
then with Nichijou it's everything from the deer fighting with the principal to gags with the girls and then all the side characters
MCA holds steady in my brain coz there's bits with everyone's eye abilities coming into play, some of the emotionally tense or heartfelt scenes or the big final fight with the snake of clearing eyes and all events that follow
and while Sonic X is mostly a thing of nostalgia (and a part of my long time sonic fixation) there's still a ton of memorable moments that I'll always hold dear
there's other clips from anime i've never watched that are still pretty memorable but all of the above are the ones i love the most