Bugei L-6 Bainite Katana
http://www.bugei.com/swords/CustomSwords.html
"The Bainite Katana is made of a special purpose low-alloy steel. It is very resistant to bending, to the point of near unbreakability. These blades can be made lighter and thinner and still remain stronger than conventional steel or 1086. The blades are also springy rather than soft, they will flex more than a normal blade, but the shape will not be altered. These blades are excellent for tameshigiri as well as general sword work." Modern alloys and techniques (well not so much modern as "not ancient") to make what is arguably the ultimate katana. Forget the days of folding steel (unless you like that kind of thing, want a certain finish, or just have a lot of time) or gimmicky notions of making ceramic-titanium-industrial diamond swords... this sword has all the best properties of a katana in spades!
(aside from edge retention... probably one of the least important factors for an effective katana) Yum.
I know this thread's not about legalities, but damn do they put a cramp on the designing process. The Tales of the Gun episode about "Magnificent Failures" and "Gun Oddities" showed all sorts of crazy gadget guns... granted most of them might not be practical, but every now and then a gem's gotta appear.
My own submission... I dunno, practical and stylish armor? Both defensive, offensive, and legal? So far for me, that's limited to steel tipped boots (protection from having my leading foot stomped on) and leather coats... but I'm fairly naked in the Summer.
Maybe if the 80's return and Goth becomes mainstream, chains, gauntlets, spikes, and pads all come back... but then God help us all!