Very common trope in RPG games as your characters near endgame. Their very high levels usually negate the flaws and when the cannon becomes anything but glass you're in for some serious ass kicking.
Bretonnian Knights in the Warhammer Fantasy. Fastest of all heavy cavalry - and also the hardest hitting. They can take almost anything head on, and especially the Grail Knights are amongst the best troops in the game. The Bretonnian army is balanced by the fact that their infantry is mostly crap
Also Ogres, who can move 12 inches per turn and can get up to 12 attacks on the first turn of combat. Ouch. Of course, this doesn't change the fact that their army still isn't exactly considered powerful due to high costs per unit, low morale and dubious magical power.
Lizardmen Saurus Warriors and Temple Guard start out as a Mighty Glacier with high durability and terrible initiative, but judicious application of Light magic by a friendly Slann can make things a lot more vicious. A unit of Temple Guard powered up with Birona's Timewarp can move as fast as cavalry and dish out three strength 5 attacks which always strike first each. This is generally somewhere in the vicinity of a horrible nightmare for any close combat army, since a Temple Guard unit in these circumstances can be charged in the rear by a full-scale horde and win.
Everyone in Warhammer 40,000 who isn't a squishy little space elf or Puny Earthling. The Space Marines aren't lightning, but they are repeatedly and consistently noted to be faster and more agile than nine-feet transhumans in bulky Powered Armor seem to have any right to be. Fear the Orks who discover red Celtic woad.
Abaddon is sort of a mixed bag since he has high initiative, but he moves slowly since he's in terminator armor.
Logan Grimnar would like to digress. During the Inquisition and Grey Knights' assault on Fenris, he combines this trope with Unstoppable Rage, being able to sprint in Terminator Armor. Let that sink in for a moment: the guy is so thoroughly pissed that he is able to run in armor that is so heavy that even Astartes are only able to trudge slowly when wearing it.
The Tau XV104 is an enormous Crisis suit with five wounds, toughness 6, defences that are at minimum on par with a Terminator, vehicle-shredding close combat power from its monstrous creature status, some of the most goofily huge guns in an army noted for its massive firearms, and yet is still able to fly with a lot more agility than anything the size of a small building, with nearly no ability to see below the horizon line, has any right to. Especially if it uses its nova charge to increase its booster speed for that turn.
Everyone who isn't a squishy little space elf? Whoever wrote that has obviously never faced a Saim-Hann Eldar army list. Like most Eldar units, they're fast and pack a decent amount of firepower, but bike Guardians get a save from the bikes too. Shining Spears are Aspect Warriors with bikes and special laser-shooting lances, making them killy against vehicles and they hit like freight-trains on the charge, too (after the momentum has been cancelled out though, they crumple). Eldar tanks like the Falcon and Fire Prism are deceptively bruiser-ish, boasting a nice array of heavy weapon choices, along with holo-fields, star engines and other little trinkets. A properly-built Eldar skimmer list both takes and dishes out big hits - at range, at least - and on a big table with a player who knows what he's doing, it's almost impossible to beat. The weakness of this army is that it is expensive, both in points (so you won't be fielding many models) and cash.
Eldar are this compared to humans. Eldar are blindingly fast and seem to move with an almost inhuman grace, and to them, humans move in slow motion. Their civilians can keep up with Space Marines, and don't get started on their close combat specialists. And although their lithe frames and slender limnbs wouldn't suggest it, they're just as strong as we are thanks to a very efficient musculature system. The Phoenix Lord Jain Zar is this compared to other Eldar: in Void Stalker, the protagonists initially believed they could hear rain falling, but it was getting gradually louder. They entered a state as close as an Astartes can get to an Oh Crap when they realised that the "rain" was actually her footfall, running straight towards them.
The Necrons in Warhammer 40,000 exhibit shades of this on the ground, if they go for a teleportation-heavy strategy, but their fleet is the utter embodiment of this trope in space-pound for pound, Necron ships are among the fastest and most maneuverable in the galaxy, rivaling and at times surpassing even the Eldar fleets. Pound for pound, Necron ships are also among the toughest nuts in the galaxy to crack. However, these advantages come at the price of lacking firepower and paying dearly for the damage the ships do take.
The lack of firepower is only for Battlefleet Gothic. In the fluff, a small escort ship can take on a small fleet by itself, destroying it before it has a chance to react (specific incident from Cain's Last Stand).
The Barbarian in edition 3.5''. They have the highest hit points, can wear up to medium level armor, rage out, giving them bonuses on taking and giving damage, and use any weapon they please, which is usually a double handed sword, bludgeoning tool, or axe. To top it off, they're also the fastest unmodified class, and at higher levels, react so fast to multiple enemies that they don't get a bonus when flanking him. Including making sure that the rogue doesn't get his handy dandy backstab feature in said mob.
In 4e they still have high hit points (really only beaten out by the Warden, now), move fast, and strike VERY hard with their rages. However, their defense is middling to poor, so you're gonna need all those extra hit points.
The Fighter in Pathfinder qualifies as a Lightning Bruiser. The ability "Armor Training" allows them to increase the Max Dexterity Bonus of their armor (they get better at dodging stuff, even when they're covered in plates of steel), decrease the Armor Penalty (they get better at getting around weight issues armor has when preforming physical actions like swimming, jumping, climbing etc.) and most importantly, they can move at full tactical speed in armor. Relatively early, too (3rd level for Medium armor, 7th for Heavy armor). Essentially, a Fighter can sprint while wearing full plate armor before he's even halfway done with his class progression.
Pathfinder Monks also qualify. Leveling up, they passively gain more speed, armor, and damage. At max level, the average medium Monk can move at 90 feet in less than 10 seconds and hit like a truck while still dodging most attacks coming their way.
Though the Tarrasque is best-known for its Nigh-Invulnerability and Instant Death Radius, it's pretty slow... but once per minute, it can Rush to boost its speed to 150 feet per round, three times faster than a horse. Pathfinder's take added the Powerful Leaper ability, letting it manage surprisingly huge jumps even when not using Rush. When it is using Rush and jumping? Yikes.
Werewolves were the eminent personification of this trope. All Werewolves (even the weaker Tribes and Auspices) became at least as strong as the strongest normal human ever when in their war-form. On top of this, the Werewolf super-stat "Rage" had the default effect of giving you more actions per round on a 1-action-per-point-of-Rage-spent basis.
Vampires also had the Brujah, whose Clan Disciplines included Celerity (going fast) and Potence (being super-strong).
High Elf heavy cavalry (Silver Helms and Dragon Princes) in Warhammer Fantasy. Lightning quick and can deliver tremendous blow - almost as efficient as the Bretonnian knights. Not as durable, though, but have better initiative in combat.
Speedsters in the Hero System can approach this. Obviously they are built for speed, but a high Dex score and Skill Levels in dodging can make them very difficult to hit, and the rules for adding velocity to melee damage mean that a speedster can, if he doesn't mind having a poor chance to hit, land a punch on somebody while going fast enough to circumnavigate the globe in a single combat phase.
Monks were intended to be this in Dungeons & Dragons. They were meant to have high movement speed and hit very often. Unfortunately, the 3.5 version is often considered to be quite lacking at high levels of optimization. The 4e version does somewhat better as a relatively effective striker.
The nature of the New World of Darkness character-building system dictates these — damage is determined by Strength + skill, and speed is determined by Strength + Dexterity + 5. If you have high strength, you're quick and powerful.
Exalted: since there's nothing whatsoever preventing you from buying, say, Melee, Athletics and Resistance (for Solars), Dexterity and Stamina (for Lunars), or Malfeas and Adorjan (for Infernals), these tend to emerge quite rapidly. A Malfean soak/damage build using Adorjani run-like-the-wind and hurricane flurry magic is something you do not want to meet in a dark alley - her ridiculously high Soak and Hardness mean all but the most brutal attacks will just bounce off, and she's likely able to outrun a Bugatti Veyron and rip off enormous rains of radioactive blows. Solars are just as unpleasant, albeit more focused on technical skill and proficiency than weird Primordial power.
In 2e, there is one Lunar charm that allows them to chase down literally anyone so long as they are deliberately pursuing them. Give that to someone who can turn into a tyrannosaurus, and the results are typically very messy.
Clan Omnimechs from the Battletech game. Faster, more armored, with more and meaner guns than the Inner Sphere counterparts.
Not really. While this was said about Clan mechs back when they were first introduced to the game, much of it turned out to be hype. They still can't break the limit of how much armor a mech is allowed to carry and they run the entire gauntlet as far as speed goes (and actually the fastest Inner Sphere mechs are faster than the fastest Clan mechs). The real advantage they have is that Clan weapons are lighter and (in the case of laser weapons) more powerful than Inner Sphere weapons, which allows them to get more bang for less mass, freeing up extra mass for a bigger engine or more armor. Assuming they actually take advantage of it (which they don't always).
The Grav Tank in GURPS: Ultra-Tech can break the sound barrier, become nearly invisible and carries a massively powerful plasma cannon. If it does get hit the armor is the equivalent of several inches of hardened steel. Those stats are for a light tank.
In Blood Bowl, players with at least strength 4 and movement 6 generally fill this mold, especially if they also have a decent agility. Most of them are balanced by being horribly expensive and limited in number. Vampires (movement 6, strength 4, agility 4, armour 8) are perhaps the most lightning bruiser of them all, but suffer from Blood Lust that gives them a 1/6 chance of delaying whatever they're supposed to be doing in order to feed.