Topic is self explanatory, choices are rather limitless ;p note "ninja gear" is not a weapon, and no, you don't have to know how to use it. (even though i know how to use these, heh.)

My personal favourite would be razor-chain-link(meaning the links in the chain are barbed, kind of like mix of barb wire and chain links) whips with hooks on the end.
Why?
Because it's sadistic and multi use tool :P And no, i didn't get idea from the newest Mortal Kombat, they've been around for a quite long while anyway, it's just one of the less known martial weapons.
Multi use?
It's both defensive and offensive in a rather balanced way, if you're not creative you may ask how can it be defensive, the answer is simple, it/they (if having 2 instead of one) can be wrapped around wrists, working as good defense as a thickened chain mail armor :P yet even when in defensive, the hooks can be used as a weapon, and they protect your hands.