Ghost in the Shell: both films, as well as Stand Alone Complex (and, for that matter Solid State Society). The reboot/rehash/new adaptation didn't work for me though, which is still a puzzle - it could have been more chewy if they threw in as much to deal with, figure out, and get to grips with.
Dragonball Z (the uncut DVDs over the mangled broadcast versions).
Vintage run of Fist of the North Star, at least up until the entirely underwhelming last few episodes where it all got a bit too wishy-washy. It lost something when the story settled down and bodies stopped exploding in blood every few minutes.
FLCL. If you don't still laugh thinking about the "wrong hole, wrong hole" scene then you need to rewatch the series. It is short, glorious, absolutely mental fun.
Perfect Blue. Not that I'm entirely certain I understood it all, but that's probably why I keep going back to it.
And Urotsukidōji: Legend of the Overfiend - this came out at just the right time to make me interested in anime originally. I'm guessing that many, many fans of anime found this to be their "holy shit" moment when it was released.
