Well,we could have exploding plasma frisbee launchers...But Tribes already got those. Called Spinfusors.
Here's some awesome Sci-Fi for ya. A missile launcher. Loads one primary shell. After a certain amount of time has passed,the warhead arms,and releases five smaller missiles. These have their own propulsion,and begin flight of their own. Again,after some time has passed,their warheads arm,and then each spits out ten bomblets,which detonate on impact. If the primary and secondary missiles hit anything with their warheads armed,they blow up,too.
That is 56 explosions per pull of the trigger,just from the munitions alone! And with science fiction,we'd have the materials to make it happen. I call it... The Ragnarok MIRV Launcher.
Now,as far as energy weapons are concerned...Realistically,lasers are piss-poor weapons,if they fire in pulses. A tiny cauterized wound. Little to no trauma,no bleedout. Unless you boil the brain or hit the heart,they're still coming. Now,let's make a weapon that makes a constant beam of deadly light. Now,you can cut up your targets with an uninterrupted coherent beam. Be the Buther of 3033!
And finally,something fun.
Quite simply,a ship mounted coaxial weapon that folds the space in front of it inside-out. I'll leave you to imagine just how this'll be fun and useful as a weapon.