To make melee weaponry useful in the future, you just need to make it so that ranged weaponry is ineffective. If, in the modern day, we invented a material that could withstand any small arms at anything but point blank range, then all modern military combat would suddenly be taking place really close up. And if you have to stand four feet from someone in order to get a bullet through their armour, why use a gun? It can jam, has to be reloaded, etc. You might as well use something like a sword (assuming, of course, that a sword could penetrate this wonder armour that stops machine guns and assault rifles).
The jedi and sith are a great example of this; given that they can deflect, block or dodge projectile weaponry, they resort to melee weaponry to fight one another.
If you want an actual design of some silly future weapon, I'd go for something that messes around the gravity. If you could manipulate gravity you could destabilise the particles of something you struck, or you could perhaps massively increase the weight of the item you're hitting something with, making your sword hit them with the mass of a garbage truck.