Most fun moment is definitely the amounts of 4 player madness New Super Mario Bros Wii has given me the last year. Everything is better when it's shared!
Most magical Mario moment, I don't know. There are so many quality Mario games that I just don't know. Super Mario Bros 3 and World always leaves me with a weird feeling, they're games I played with a bunch of people that I've lost contact with or where my relationship to them has really changed, so it's just weird to think about really. Definitely had lost of great moments with those two games. The sun in the desert world still makes me cream my pants, and not in the front of the pants. In the back. :( Same with that stupid fish in world 3. I'm pretty sure I cried a few times, what a horrible way to go.
Super Mario 64 is beyond awesome in itself, such an open and free game. Downright magical. Same with Super Mario RPG, although it's a game I don't have the power of nostalgia attached to, I played it when I was quite old. I'd totally fall in love with that game as a kid, though. Still, a great game, but I can't really point at any specific moments.
I seriously admire then for still being able to crank out great games, Super Mario Galaxy 2 was just plain awesome. Gotta love Mario.