The Flying Guillotine. Oddjob's Hat. The Noisy Cricket. The Power Glove.
The most common and archetypal weapons have earned their status generally because they're the most tried-and-true, but they all melt into the background upon the arrival of that one troublemaker with the unique weapon nobody's ever seen before.
I'm talking about exotic weapons: those instruments of war so obscure and exacting that only the most dedicated can bring them to bear against their hapless foes. The use of such weapons is rarely seen, since the cost of a feat is generally not worth whatever they have to offer, but the psychological edge of someone wielding a weapon that A) Is unknown to you, and B) They're convinced is worth the cost of a feat, can sometimes be power enough.
So the inevitable question stands - which exotic weapons are worth it? Surely the price of a feat isn't worth one extra point of damage or a +2 bonus to disarm... nevermind the roleplaying nightmare of tracking down a blacksmith able and willing to forge your Kaorti Resin Elven Courtblade. There is no obscure weapon out there that closes the gap between magic and mundane, no matter how many times they fold the steel, but there is the occasional standout for combat utility or sheer brute force. At the very least, the use of a unique weapon can provide interest and roleplay potential to a character, or distinctiveness and mystique to an NPC. So if you're planning to do it anyway, might as well pick up something that can perform decently well while you're at it.