Terrakion
While I thought a speedy broken Steel Uber type had to make the list (and voted Genesect for #6), now that Exca is on the list, I'm throwing my vote behind Terrakion. Strong Fighting types DEFINED this metagame-- to the point where one would say that the Dragon-, Steel-, Water- three kings of DP were joined by Fighting in BW to make not 3, but 4 top types to rule OU.
BW added a ton of Fighting types, and they were a driving force throughout the generation, with their power and awesome STAB attacks backed by fantastic bulk or Speed. Fighting type resisted the 3 dangerous threats of Dark-, Bug-, and Rock (Pursuit, U-Turn, SR), and came with no common weaknesses (with the otherwise mediore Psychic attacks becoming more popular in BW JUST because of the dominance of Fighting-types). Their STAB attacks paired almost flawlessly with 6 different types, and was desirable coverage when paired with EVERY other type except Ground (and hell, Lando-I even got banned because of Ground + Fighting + HP Ice coverage, lol). Almost any type could be made better just by pairing it with Fighting.
But while Verizion, Mienshao, and Scrafty were all considered a part of this force in BW, all of them were kicked to the curb by continued testing. Even Konkeldurr, Lucario, and Infernape could barely endure this trial by weather of the tough OU meta that left one as an obvious king of Fighters-- brute strength, raw stats, and near flawless STABs proved pivotal in making Terrakion the obvious king bull. Of all the early Fighting types, only 1 could prove itself an enduring top threat throughout BW (with Breloom holding that position only during the initial Darkrai Metagame, and then after getting Technician).
Terrakion's power was sooo incredible, that unlike anything up until now-- GF designed a Pokemon JUST to control it (Lando-T)! lol
In BW2, Keldeo was released, and Terrak's little brother filled the void left by the competitors it had kicked out, and the two of them held the throne-- ensuring that no one would forget the defining role of Fighting types in the metagame. I think Terrakion (or at least Keldeo) needs to make this list as a representative of this legacy.