My Blastoise and Mewtwo. Though I had a Charizard in my Blue version, for some reason I never trained it all the way (though I liked it better)...meh.
Blastoise:
Hydro Pump
Surf
Ice Beam
Earthquake--not the best moveset, but it had wickedly good stats, and I still can't figure out why.
Mewto:
Psychic
Recover
Swift
Barrier/Shadow Ball--when I traded it to my Crystal it got Shadow Ball. This thing was friggin unbeatable. It defeated other lvl 100 Mewtwos no-problemo. Maybe it went through enough games and enough badges...well, I lost both of them, as well as my Lvl. 100 Arcanine, Electabuzz, Pidgeot, and Victreebell, when I restarted the Crystal Version :(.