Scorpions spear and Sub-Zeros ice ball are obvious classics but I think my favourite is probably Ermac's Telekinetic slam. I also really like Rain's super roundhouse nothing better than booting someone across the screen.
It's not really a special move, but more a command move...
I always loved spinny flip kicks and as a Jade fan, I've wanted for her to have one as well. And in MK9 she finally got one with Pole Vault. It's nothing fancy, but damn does it look cool and feel so satisfying when using it.
I’m going to go with Kano-Ball, since he’s who I played the most in MK9. That move always felt mystical to me since I couldn’t figure out how to do it in MK1 except by accident. And it’s just so ridiculous, I love it!
Sektor's Teleport punch, I love the pose he does with his arm over his chest as he slips into the ground, just to appear infront of you a second later to break your chin.
A runner up would be any of Noob's moves were he throws Saibot at you.