The Iaito in Dark Souls is pretty high up there for me. The animation of its strong-attack, both one and two-handed, makes every kill seem so much more stylish. Sheath the blade, and either take a quick step forward or a running dash forward before quick-drawing and cutting the enemy down. Bonus point for ending up behind them as they collapse while you sheath the blade.
Give me any sniper rifle in any shooter, and I'm in paradise. Bolt action, semi-automatic, scope, dot-sight, whatever--if I can line up the perfect shot from a distance and take them out without ever knowing I was there, that's all I need.
Last, if anyone remembers Golden Sun: The Lost Age, then there are too many to choose from. The Sol Blade, Lachesis' Rule, Firebrand, Kikuichimonji, Thanatos Mace, etc. So many unique unleashes, and they're just too cool to not want to see all of them.