Lucky Star and K-on for CGDCT
Evangelion for meta-commentary and deconstruction, to the point that future works that qualify often get called the “Evangelion of <genre>”
Fullmetal Alchemist Brotherhood and Attack on Titan for battle shounen
Bocchi the Rock for girls band anime, specifically
Lupin III: The Castle of Cagliostro for pretty much all of Ghibli
Akira for 90s anime


I was not watching anime at the time they aired, but I remember it was that, Haruhi, and Kimi ni Todoke together
I suspect without Toradora there would be no Horimiya, which was my introduction to Slice of Life. Without it, my anime tastes probably wouldn’t have moved beyond sexy elves into genuine quality with things like Your Lie In April and Anohana.