Dragon: Roar Of Time (150) - Dialga
Fire: V-create (180) - Victini and Rayquaza. The strongest non-signature Fire move is Eruption at 100% (150).
Water: Hydro Cannon/Water Spout at 100% HP (150) - Hydro Cannon shouldn't be used and Kyogre for Water Spout
Grass: Frenzy Plant (150) - Grass starters, but it shouldn't be used.
Ground: Magnitude 10 (150), otherwise it is a Bone Rush hitting 5 times (125), and next is Earthquake (100) - Magnitude and Bone Rush shouldnt be used, lots of Pokemon abuse EQ
Poison: Gunk Shot (120) - Probably shouldn't be used, but Pokemon like Muk and Arbok can abuse it for extra power.
Flying: Sky Attack (140) - Shouldnt be used
Fighting: Reversal at very low HP (200), otherwise Focus Punch (150) - Dugtrio, Breloom
Ice: Ice Ball on it's fifth hit , otherwise Freeze Shock/Ice Burn (140) - Ice Ball shouldnt be used, Kyurem for the latter 2. Besides Freeze Shock/Ice Burn, Blizzard takes the spot of the strongest Ice type move.
Dark: Foul Play (95) - Umbreon
Rock: Head Smash/Rock Wrecker (150) - Rampardos, Aggron, Rock Wrecker should not be used
Steel: Doom Desire (140) - Jirachi. The strongest non-signature Steel type attack is Iron Tail (100).
Psychic: Psycho Boost (140) - Deoxys. The strongest non-signature Psychic attack is Psychic (90).
Electric: Bolt Strike (130) - Zekrom, Victini, the strongest non-signature Electric type attack is Thunder/Zap Cannon (120)
Bug: Fury Cutter at max power (160), otherwise Megahorn (120) - Fury Cutter should not be used - Heracross, Rhyperior, Samurott.
Normal: Explosion (250) - Not really the best, Bronzong.
Ghost: Shadow Force (120) - Giratina, Arceus. The strongest non-signature Ghost type attack is Shadow Ball (80).
Exlcuding OHKO Atacks, list in no real order. I'll put them in alphabetical order later today ;) Also note that I did not post like, every Pokemon that can learn them, just some notable users.