Fire Blast, Recover, and Hyper Beam were all really cool for me, at least. In future generations, the Hyper Beam didn't have the multicolored particles, which I really liked. A similar instance of that was Ice Beam, where they changed it from the crystal particles to a straight beam. Disappointing...
With the Recover orbs, I could always feel that sense of "Gahhhhhh" everytime someone used it. And that rising sound effect just was icing on the already awesome cake.
And Fire Blast has always been amazing. Having a giant Kanji symbol that says "FIRE" when you use it is just wicked.